Electrochromic rearview mirror assembly incorporating a display/signal light

ABSTRACT

According to one embodiment of the present invention, an electrochromic rearview mirror assembly for a vehicle includes an electrochromic mirror having a variable reflectivity, a glare sensor for sensing levels of light directed towards the front element from the rear of the vehicle, an ambient sensor for sensing levels of ambient light, a display positioned behind the partially transmissive, partially reflective portion of the reflector for displaying information therethrough.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/777,846, filed on Feb. 12, 2004 now U.S. Pat. No. 7,042,616; which isa continuation of U.S. patent application Ser. No. 10/115,860, filed onApr. 3, 2002, now U.S. Pat. No. 6,700,692; which is acontinuation-in-part of U.S. patent application Ser. No. 09/994,218,filed on Nov. 26, 2001, now U.S. Pat. No. 6,512,624; which is acontinuation of U.S. patent application Ser. No. 09/311,955, filed onMay 14, 1999, now U.S. Pat. No. 6,356,376; which is acontinuation-in-part of U.S. patent application Ser. No. 09/206,788,filed on Dec. 7, 1998, now U.S. Pat. No. 6,166,848; which is acontinuation-in-part of U.S. patent application Ser. No. 09/197,400,filed on Nov. 20, 1998, now U.S. Pat. No. 6,111,684; which is acontinuation-in-part of U.S. patent application Ser. No. 09/114,386,filed on Jul. 13, 1998, now U.S. Pat. No. 6,064,508; which is acontinuation of U.S. patent application Ser. No. 08/832,587, filed onApr. 2, 1997, now U.S. Pat. No. 5,818,625, the entire disclosures ofwhich are herein incorporated by reference.

Said U.S. patent application Ser. No. 09/206,788 is also acontinuation-in-part of U.S. patent application Ser. No. 09/175,984filed on Oct. 20, 1998, now U.S. Pat. No. 6,111,683; which is acontinuation-in-part of U.S. patent application Ser. No. 08/831,808filed on Apr. 2, 1997, now U.S. Pat. No. 5,825,527, the entiredisclosures of which are incorporated herein by reference.

Said U.S. patent application Ser. No. 10/115,860 is also acontinuation-in-part of U.S. patent application Ser. No. 09/425,792filed on Oct. 22, 1999, now U.S. Pat. No. 6,441,943; which is acontinuation-in-part of the above-referenced U.S. patent applicationSer. No. 09/311,955 filed on May 14, 1999, now U.S. Pat. No. 6,356,376;and which claims priority to U.S. Provisional Patent Application No.60/124,493 filed on Mar. 15, 1999, the entire disclosures of which areincorporated herein by reference.

Said U.S. patent application Ser. No. 10/115,860 is also acontinuation-in-part of U.S. patent application Ser. No. 09/918,213filed on Jul. 30, 2001, now abandoned; which is a continuation of U.S.patent application Ser. No. 09/560,849 filed on Apr. 28, 2000, now U.S.Pat. No. 6,268,950; which is a continuation of U.S. patent applicationSer. No. 09/375,136 filed on Aug. 16, 1999, now U.S. Pat. No. 6,057,956;which is a continuation of U.S. patent application Ser. No. 08/834,783filed Apr. 2, 1997, now U.S. Pat. No. 5,940,201, the entire disclosuresof which are incorporated herein by reference.

Priority under 35 U.S.C. §120 and §119(e) is hereby claimed upon each ofthe above-identified patent applications.

BACKGROUND OF THE INVENTION

This invention relates to electrochromic devices and rearview mirrorassemblies for motor vehicles and, more particularly, to improvedelectrochromic rearview mirror assemblies.

Heretofore, various rearview mirrors for motor vehicles have beenproposed which change from the full reflectance mode (day) to thepartial reflectance mode(s) (night) for glare-protection purposes fromlight emanating from the headlights of vehicles approaching from therear. Among such devices are those wherein the transmittance is variedby thermochromic, photochromic, or electro-optic means (e.g., liquidcrystal, dipolar suspension, electrophoretic, electrochromic, etc.) andwhere the variable transmittance characteristic affects electromagneticradiation that is at least partly in the visible spectrum (wavelengthsfrom about 3800 Å to about 7800 Å). Devices of reversibly variabletransmittance to electromagnetic radiation have been proposed as thevariable transmittance element in variable transmittance light filters,variable reflectance mirrors, and display devices, which employ suchlight filters or mirrors in conveying information. These variabletransmittance light filters have included windows.

Devices of reversibly variable transmittance to electromagneticradiation, wherein the transmittance is altered by electrochromic means,are described, for example, by Chang, “Electrochromic andElectrochemichromic Materials and Phenomena,” in Non-emissiveElectrooptic Displays, A. Kmetz and K. von Willisen, eds. Plenum Press,New York, N.Y. 1976, pp. 155-196 (1976) and in various parts ofElectrochromism, P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCHPublishers, Inc., New York, N.Y. (1995). Numerous electrochromic devicesare known in the art. See, e.g., Manos, U.S. Pat. No. 3,451,741;Bredfeldt et al., U.S. Pat. No. 4,090,358; Clecak et al., U.S. Pat. No.4,139,276; Kissa et al., U.S. Pat. No. 3,453,038; Rogers, U.S. Pat. Nos.3,652,149, 3,774,988 and 3,873,185; and Jones et al., U.S. Pat. Nos.3,282,157, 3,282,158, 3,282,160 and 3,283,656.

In addition to these devices, there are commercially availableelectrochromic devices and associated circuitry, such as those disclosedin U.S. Pat. No. 4,902,108, entitled “SINGLE-COMPARTMENT, SELF-ERASING,SOLUTION-PHASE ELECTROCHROMIC DEVICES SOLUTIONS FOR USE THEREIN, ANDUSES THEREOF,” issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No.1,300,945, entitled “AUTOMATIC REARVIEW MIRROR SYSTEM FOR AUTOMOTIVEVEHICLES,” issued May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No.5,128,799, entitled “VARIABLE REFLECTANCE MOTOR VEHICLE MIRROR,” issuedJul. 7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled“ELECTRO-OPTIC DEVICE,” issued Apr. 13, 1993, to H. J. Byker et al.;U.S. Pat. No. 5,204,778, entitled “CONTROL SYSTEM FOR AUTOMATIC REARVIEWMIRRORS,” issued Apr. 20, 1993, to J. H. Bechtel; U.S. Pat. No.5,278,693, entitled “TINTED SOLUTION-PHASE ELECTROCHROMIC MIRRORS,”issued Jan. 11, 1994, to D. A. Theiste et al.; U.S. Pat. No. 5,280,380,entitled “UV-STABILIZED COMPOSITIONS AND METHODS,” issued Jan. 18, 1994,to H. J. Byker; U.S. Pat. No. 5,282,077, entitled “VARIABLE REFLECTANCEMIRROR,” issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376,entitled “BIPYRIDINIUM SALT SOLUTIONS,” issued Mar. 15, 1994, to H. J.Byker; U.S. Pat. No. 5,336,448, entitled “ELECTROCHROMIC DEVICES WITHBIPYRIDINIUM SALT SOLUTIONS,” issued Aug. 9, 1994, to H. J. Byker; U.S.Pat. No. 5,434,407, entitled “AUTOMATIC REARVIEW MIRROR INCORPORATINGLIGHT PIPE,” issued Jan. 18, 1995, to F. T. Bauer et al.; U.S. Pat. No.5,448,397, entitled “OUTSIDE AUTOMATIC REARVIEW MIRROR FOR AUTOMOTIVEVEHICLES,” issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No.5,451,822, entitled “ELECTRONIC CONTROL SYSTEM,” issued Sep. 19, 1995,to J. H. Bechtel et al. Each of these patents is commonly assigned withthe present invention and the disclosures of each, including thereferences contained therein, are hereby incorporated herein in theirentirety by reference. Such electrochromic devices may be utilized in afully integrated inside/outside rearview mirror system or as separateinside or outside rearview mirror systems.

FIG. 1 shows a typical electrochromic mirror device 10, having front andrear planar elements 12 and 16, respectively. A transparent conductivecoating 14 is placed on the rear face of the front element 12, andanother transparent conductive coating 18 is placed on the front face ofrear element 16. A reflector (20 a, 20 b and 20 c), typically comprisinga silver metal layer 20 a covered by a protective copper metal layer 20b, and one or more layers of protective paint 20 c, is disposed on therear face of the rear element 16. For clarity of description of such astructure, the front surface of the front glass element is sometimesreferred to as the first surface, and the inside surface of the frontglass element is sometimes referred to as the second surface. The insidesurface of the rear glass element is sometimes referred to as the thirdsurface, and the back surface of the rear glass element is sometimesreferred to as the fourth surface. The front and rear elements are heldin a parallel and spaced-apart relationship by seal 22, thereby creatinga chamber 26. The electrochromic medium 24 is contained in space 26. Theelectrochromic medium 24 is in direct contact with transparent electrodelayers 14 and 18, through which passes electromagnetic radiation whoseintensity is reversibly modulated in the device by a variable voltage orpotential applied to electrode layers 14 and 18 through clip contactsand an electronic circuit (not shown).

The electrochromic medium 24 placed in space 26 may includesurface-confined, electrode position-type or solution-phase-typeelectrochromic materials and combinations thereof. In an allsolution-phase medium, the electrochemical properties of the solvent,optional inert electrolyte, anodic materials, cathodic materials, andany other components that might be present in the solution arepreferably such that no significant electrochemical or other changesoccur at a potential difference which oxidizes anodic material andreduces the cathodic material other than the electrochemical oxidationof the anodic material, electrochemical reduction of the cathodicmaterial, and the self-erasing reaction between the oxidized form of theanodic material and the reduced form of the cathodic material.

In most cases, when there is no electrical potential difference betweentransparent conductors 14 and 18, the electrochromic medium 24 in space26 is essentially colorless or nearly colorless, and incoming light(I_(o)) enters through front element 12, passes through transparentcoating 14, electrochromic containing chamber 26, transparent coating18, rear element 16, reflects off layer 20 a and travels back throughthe device and out front element 12. Typically, the magnitude of thereflected image (I_(R)) with no electrical potential difference is about45 percent to about 85 percent of the incident light intensity (I_(o)).The exact value depends on many variables outlined below, such as, forexample, the residual reflection (I′_(R)). from the front face of thefront element, as well as secondary reflections from the interfacesbetween: the front element 12 and the front transparent electrode 14,the front transparent electrode 14 and the electrochromic medium 24, theelectrochromic medium 24 and the second transparent electrode 18, andthe second transparent electrode 18 and the rear element 16. Thesereflections are well known in the art and are due to the difference inrefractive indices between one material and another as the light crossesthe interface between the two. If the front element and the back elementare not parallel, then the residual reflectance (I′_(R)) or othersecondary reflections will not superimpose with the reflected image(I_(R)) from mirror surface 20 a, and a double image will appear (wherean observer would see what appears to be double (or triple) the numberof objects actually present in the reflected image).

There are minimum requirements for the magnitude of the reflected imagedepending in whether the electrochromic mirrors are placed on the insideor the outside of the vehicle. For example, according to currentrequirements from most automobile manufacturers, inside mirrorspreferably have a high end reflectivity of at least 70 percent, andoutside mirrors must have a high end reflectivity of at least 35percent.

Electrode layers 14 and 18 are connected to electronic circuitry whichis effective to electrically energize the electrochromic medium, suchthat when a potential is applied across the transparent conductors 14and 18, electrochromic medium in space 26 darkens, such that incidentlight (I_(o)) is attenuated as the light passes toward the reflector 20a and as it passes back through after being reflected. By adjusting thepotential difference between the transparent electrodes, such a devicecan function as a “gray-scale” device, with continuously variabletransmittance over a wide range. For solution-phase electrochromicsystems, when the potential between the electrodes is removed orreturned to zero, the device spontaneously returns to the same,zero-potential, equilibrium color and transmittance as the device hadbefore the potential was applied. Other electrochromic materials areavailable for making electrochromic devices. For example, theelectrochromic medium may include electrochromic materials that aresolid metal oxides, redox active polymers, and hybrid combinations ofsolution-phase and solid metal oxides or redox active polymers; however,the above-described solution-phase design is typical of most of theelectrochromic devices presently in use.

Even before a fourth surface reflector electrochromic mirror wascommercially available, various groups researching electrochromicdevices had discussed moving the reflector from the fourth surface tothe third surface. Such a design has advantages in that it should,theoretically, be easier to manufacture because there are fewer layersto build into a device, i.e., the third surface transparent electrode isnot necessary when there is a third surface reflector/electrode.Although this concept was described as early as 1966, no group hadcommercial success because of the exacting criteria demanded from aworkable auto-dimming mirror incorporating a third surface reflector.U.S. Pat. No. 3,280,701, entitled “OPTICALLY VARIABLE ONE-WAY MIRROR,”issued Oct. 25, 1966, to J. F. Donnelly et al. has one of the earliestdiscussions of a third surface reflector for a system using a pH-inducedcolor change to attenuate light.

U.S. Pat. No. 5,066,112, entitled “PERIMETER COATED, ELECTRO-OPTICMIRROR,” issued Nov. 19, 1991, to N. R. Lynam et al., teaches anelectro-optic mirror with a conductive coating applied to the perimeterof the front and rear glass elements for concealing the seal. Although athird surface reflector is discussed therein, the materials listed asbeing useful as a third surface reflector suffer from one or more of thefollowing deficiencies: not having sufficient reflectivity for use as aninside mirror, or not being stable when in contact with a solution-phaseelectrochromic medium containing at least one solution-phaseelectrochromic material.

Others have broached the topic of a reflector/electrode disposed in themiddle of an all solid state-type device. For example, U.S. Pat. Nos.4,762,401, 4,973,141, and 5,069,535 to Baucke et al. teach anelectrochromic mirror having the following structure: a glass element, atransparent (ITO) electrode, a tungsten oxide electrochromic layer, asolid ion conducting layer, a single layer hydrogen ion-permeablereflector, a solid ion conducting layer, a hydrogen ion storage layer, acatalytic layer, a rear metallic layer, and a back element (representingthe conventional third and fourth surface). The reflector is notdeposited on the third surface and is not directly in contact withelectrochromic materials, certainly not at least one solution-phaseelectrochromic material and associated medium. Consequently, it isdesirable to provide an improved high reflectivity electrochromicrearview mirror having a third surface reflector/electrode in contactwith a solution-phase electrochromic medium containing at least oneelectrochromic material.

In the past, information, images or symbols from displays, such asvacuum fluorescent displays, have been displayed on electrochromicrearview mirrors for motor vehicles with reflective layers on the fourthsurface of the mirror. The display is visible to the vehicle occupant byremoving all of the reflective layer on a portion of the fourth surfaceand placing the display in that area. Although this design worksadequately due to the transparent conductors on the second and thirdsurface to impart current to the electrochromic medium, presently nodesign is commercially available which allows a display device to beincorporated into a mirror that has a reflective layer on thethird-surface. Removing all of the reflective layer on the third surfacein the area aligned with the display area or the glare sensor areacauses severe residual color problems when the electrochromic mediumdarkens and clears because, although colorization occurs at thetransparent electrode on the second surface, there is no correspondingelectrode on the third surface in that corresponding area to balance thecharge. As a result, the color generated at the second surface (acrossfrom the display area or the glare sensor area) will not darken or clearat the same rate as other areas with balanced electrodes. This colorvariation is significant and is very aesthetically unappealing to thevehicle occupants.

Related U.S. Pat. No. 6,166,848 discloses several possible solutions tothe above-noted problems pertaining to utilizing a display incombination with an electrochromic mirror. Specifically, this patentdiscloses utilizing a transflective (partially transmissive, partiallyreflective) electrode on the third surface of the electrochromic mirrorstructure. This provides electrical conductivity of the electrode withinthe electrochromic cell in front of the display while not requiring anon-reflective region in the mirror to be present.

A problem associated with providing a transflective layer in front ofthe display (whether it is on the third or fourth surface of theelectrochromic structure) is that it is difficult to obtain an adequatecontrast ratio between the light originating from the display and theambient light that reflects off the transflective layer. This isparticularly true in daylight ambient lighting conditions where thelight from the ambient environment is very bright and reflects off thetransflective layer over the entire surface of the mirror including thatregion through which light from the display is transmitted. Accordingly,there exists the need for a solution that increases the contrast ratioduring all ambient light conditions.

Similar problems exist for outside rearview mirror assemblies thatinclude signal lights, such as turn signal lights, behind the rearsurface of the mirror. Examples of such signal mirrors are disclosed inU.S. Pat. Nos. 5,207,492, 5,361,190, and 5,788,357. By providing a turnsignal light in an outside mirror assembly, a vehicle, or other vehiclestravelling in the blind spot of the subject vehicle, will be more likelyto notice when the driver has activated the vehicle's turn signal andthereby attempt to avoid an accident. Such mirror assemblies typicallyemploy a dichroic mirror and a plurality of red LEDs mounted behind themirror as the signal light source. The dichroic mirror includes a glasssubstrate and a dichroic reflective coating provided on the rear surfaceof the glass plate that transmits the red light generated by the LEDs aswell as infrared radiation while reflecting all light and radiationhaving wavelengths less than that of red light. By utilizing a dichroicmirror, such mirror assemblies hide the LEDs when not in use to providethe general appearance of a typical rearview mirror, and allow the redlight from such LEDs to pass through the dichroic mirror and be visibleto drivers of vehicles behind and to the side of the vehicle in whichsuch a mirror assembly is mounted. Examples of such signal mirrors aredisclosed in U.S. Pat. Nos. 5,361,190 and 5,788,357.

In daylight, the intensity of the LEDs must be relatively high to enablethose in other vehicles to readily notice the signal lights. Because theimage reflected toward the driver is also relatively high in daylight,the brightness of the LEDs is not overly distracting. However, at nightthe same LED intensity could be very distracting, and hence, potentiallyhazardous. To avoid this problem, a day/night sensing circuit is mountedin the signal light subassembly behind the dichroic mirror to sensewhether it is daytime or nighttime and toggle the intensity of the LEDsbetween two different intensity levels. The sensor employed in theday/night sensing circuit is most sensitive to red and infrared light soas to more easily distinguish between daylight conditions and the brightglare from the headlights of a vehicle approaching from the rear. Hence,the sensor may be mounted behind the dichroic coating on the dichroicmirror.

The dichroic mirrors used in the above-described outside mirrorassemblies suffer from the same problems of many outside mirrorassemblies in that their reflectance cannot be dynamically varied toreduce nighttime glare from the headlights of other vehicles.

Although outside mirror assemblies exist that include signal lights andother outside mirror assemblies exist that include electrochromicmirrors, signal lights have not been provided in mirror assemblieshaving an electrochromic mirror because the dichroic coating needed tohide the LEDs of the signal light typically cannot be applied to anelectrochromic mirror, particularly those mirrors that employ a thirdsurface reflector/electrode.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a rearview mirrorassembly for a vehicle comprises a mirror comprising a reflector havinga partially transmissive, partially reflective area. The rearview mirrorassembly further comprises a first sensor for sensing light levels; adisplay positioned behind the partially transmissive, partiallyreflective portion of the reflector for displaying informationtherethrough; and a control circuit coupled to the first sensor and thedisplay. The control circuit determines whether daytime or nighttimeconditions are present. During daytime conditions, the control circuitresponds to light levels sensed by the first sensor to control acontrast ratio of light originating from the display and lightreflecting from the partially transmissive, partially reflective area ofthe reflector.

According to another embodiment of the present invention, a displaydevice for a vehicle comprises: a light sensor for sensing ambient lightlevels; a display for displaying information to an occupant of thevehicle; and a control circuit coupled to the display and the lightsensor. The control circuit determines whether daytime or nighttimeconditions are present as a function of the ambient light level sensedby the light sensor. During daytime conditions, the control circuitvaries the brightness level of the display within a first range ofbrightness levels. During nighttime conditions, the control circuitvaries the brightness level of the display within a second range ofbrightness levels, which is different from the first range of brightnesslevels.

According to another embodiment of the present invention, a rearviewmirror assembly for a vehicle comprises: a housing; a mirror supportedby the housing; an ambient sensor supported by the housing for sensinglevels of ambient light; and a control circuit supported by the housingand coupled to the ambient sensor and coupled to a display device remotefrom the rearview mirror assembly. The control circuit determineswhether daytime or nighttime conditions are present as a function of theambient light level sensed by the ambient sensor, generates a displaybrightness control signal based upon the determination ofdaytime/nighttime condition, and transmits the display brightnesscontrol signal to the remote display device to which the remote displaydevice responds by varying its brightness level.

According to another embodiment of the present invention, a rearviewmirror assembly for a vehicle comprises: a housing adapted to be mountedto the vehicle; front and rear elements mounted in the housing, theelements each having front and rear surfaces; an electrochromic materialcontained between the elements; a transparent first electrode includinga layer of conductive material carried on a surface of one of theelements; a second electrode disposed on the front surface of the rearelement; a light emitting display assembly mounted in the housing, thedisplay assembly having a cover having a rear surface and a frontsurface that is mounted adjacent the rear surface of the rear element;and an anti-reflective structure applied to a surface of the displayassembly. Either the second electrode is a reflective electrode or aseparate reflector is disposed over substantially all of the rearsurface of the rear element. The reflective electrode/reflector ispartially transmissive and partially reflective in at least a locationin front of the display assembly.

According to another embodiment of the present invention, a rearviewmirror assembly for a vehicle comprises: a housing adapted to be mountedto the vehicle; front and rear elements mounted in the housing, theelements each having front and rear surfaces; a transparent firstelectrode including a layer of conductive material carried on a surfaceof one of the elements; a second electrode disposed on the front surfaceof the rear element; and an electrochromic material contained betweenthe elements. One of the front and rear elements comprises an organiclight emitting diode display. Either the second electrode is areflective electrode or a separate reflector is disposed oversubstantially all of the rear surface of the rear element.

According to another embodiment of the present invention, a rearviewmirror assembly for a vehicle comprises: front and rear elements eachhaving front and rear surfaces; a transparent first electrode includinga layer of conductive material carried on a surface of one of theelements; a second electrode carried on a surface of one of theelements; an electrochromic material contained between the elements andhaving a variable transmissivity; a reflector carried on a surface ofthe rear element, wherein the second electrode is integrated with thereflector when the reflector is carried on the front surface of the rearelement, at least a portion of the reflector is partially transmissiveand partially reflective; and a light emitting display assembly mountedin the housing. The display assembly is mounted adjacent the rearsurface of the rear element. A region of the reflector in front of thedisplay assembly exhibits a reflective gradient whereby the reflectivityof the reflector gradually decreases throughout at least a portion ofthe region in front of the display assembly.

According to another embodiment of the present invention, anelectrochromic device comprises: front and rear elements each havingfront and rear surfaces; a transparent first electrode including a layerof conductive material carried on a surface of one of the elements; asecond electrode carried on a surface of one of the elements; anelectrochromic material contained between the elements and having avariable transmissivity; and a reflector carried on a surface of therear element. The second electrode is integrated with the reflector whenthe reflector is carried on the front surface of the rear element. Atleast a portion of the reflector is partially transmissive and partiallyreflective. The reflector is a diffuse reflector for diffusing andreflecting light incident thereon.

According to another embodiment of the present invention, anelectrochromic mirror is provided for use in a rearview mirror assemblyhaving a light source positioned behind the electrochromic mirror forselectively projecting light therethrough. The electrochromic mirrorcomprises: front and rear spaced elements, each having front and rearsurfaces; a transparent first electrode including a layer of conductivematerial disposed on the rear surface of the front element; anelectrochromic medium contained between the elements; and a secondelectrode overlying the front surface of the rear element. The secondelectrode includes a first reflective coating and a second coating oftransparent electrically conductive material. The second electrodeincludes a region in front of the light source that is at leastpartially transmissive.

According to another embodiment of the present invention, a rearviewmirror assembly for a vehicle comprises: a housing adapted to be mountedto the vehicle; front and rear elements mounted in the housing, theelements each having front and rear surfaces; a transparent firstelectrode including a layer of conductive material carried on a surfaceof one of the elements; a second electrode disposed on the front surfaceof the rear element; an electrochromic material contained between theelements; and a computer video monitor on mirror disposed over a surfaceof one of the front and rear elements and coupled to a computer fordisplaying information provided from the computer. Either the secondelectrode is a reflective electrode or a separate reflector is disposedover substantially all of the rear surface of the rear element.

According to another embodiment of the present invention, a rearviewmirror assembly for a vehicle comprises: a housing adapted to be mountedto the vehicle; front and rear elements mounted in the housing, theelements each having front and rear surfaces; a transparent firstelectrode including a layer of conductive material carried on a surfaceof one of the elements; a second electrode disposed on the front surfaceof the rear element; an electrochromic material contained between theelements; and an electroluminescent display disposed over a surface ofone of the front and rear elements. Either the second electrode is areflective electrode or a separate reflector is disposed oversubstantially all of the rear surface of the rear element.

According to another embodiment of the present invention, anelectrochromic mirror comprises: front and rear elements each havingfront and rear surfaces, wherein at least one of the front and rearelements has a thickness ranging from about 0.5 mm to about 1.8 mm; atransparent first electrode including a layer of conductive materialcarried on a surface of one of the elements; a second electrode carriedon a surface of one of the elements; an electrochromic materialcontained between the elements and having a variable transmissivity; anda reflector carried on a surface of the rear element. The secondelectrode is integrated with the reflector when the reflector is carriedon the front surface of the rear element. At least a portion of thereflector is partially transmissive and partially reflective.

According to another embodiment of the present invention, anelectrochromic mirror comprises: front and rear spaced elements, eachhaving front and rear surfaces; a transparent first electrode includinga layer of conductive material disposed on the rear surface of the frontelement; an electrochromic medium contained between the elements; and asecond electrode overlying the front surface of the rear element. Thesecond electrode includes a layer of white gold.

According to another embodiment of the present invention, anelectrochromic rearview mirror assembly comprises: an electrochromicmirror element having a variable reflectivity; and a display devicepositioned behind the electrochromic mirror element for displayinginformation in a first color through the electrochromic mirror element.The display device comprising at least one first light source foremitting light of a second color and at least one second light sourcefor emitting light of a third color, the second and third colors beingdifferent from each other and from the first color while mixing togetherto form light of the first color.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an enlarged cross-sectional view of a prior art electrochromicmirror assembly;

FIG. 2 is a front elevational view schematically illustrating aninside/outside electrochromic rearview mirror system for motor vehicles,where the inside and outside mirrors incorporate the mirror assembly ofthe present invention;

FIG. 3 is an enlarged cross-sectional view of the inside electrochromicrearview mirror incorporating a third surface reflector/electrodeillustrated in FIG. 2, taken on the line 3-3′ thereof;

FIG. 4 is an enlarged cross-sectional view of an electrochromic mirrorincorporating an alternate embodiment of a third surfacereflector/electrode according to the present invention;

FIG. 5 a is an enlarged cross-sectional view of an electrochromic mirrorhaving an improved arrangement for applying a drive potential to thetransparent conductor on the second surface of the mirror;

FIG. 5 b is an enlarged top view of the third surface reflector of FIG.5 a;

FIG. 6 is an enlarged cross-sectional view of an electrochromic mirrorusing a cured and machine-milled epoxy seal to hold the transparentelements in a spaced-apart relationship;

FIGS. 7A-7H are partial cross-sectional views of alternativeconstructions of the electrochromic mirror according to the presentinvention as taken along line 7-7′ shown in FIG. 2;

FIG. 8 is a partial cross-sectional view of the electrochromic mirroraccording to the present invention as taken along line 7-7′ shown inFIG. 2;

FIGS. 9A-9G are partial cross-sectional views of additional alternativeconstructions of the electrochromic mirror according to the presentinvention as taken along lines 7-7′ shown in FIG. 2;

FIG. 10 is a front elevational view schematically illustrating an insideelectrochromic rearview mirror incorporating the mirror assembly of thepresent invention;

FIG. 11 is a partial cross-sectional view of the electrochromic mirrorshown in FIG. 10 taken along line 11-11′;

FIG. 12 is a perspective view of an outside automatic rearview mirrorincluding a signal light and an electrical circuit diagram in block formof an outside rearview mirror assembly constructed in accordance withthe present invention;

FIG. 13 is a front elevational view of a signal light subassembly thatmay be used in the outside mirror assembly of the present invention;

FIG. 14A is a partial cross-sectional view taken along line 14-14′ ofFIG. 12 illustrating one construction of the outside rearview mirror ofthe present invention;

FIG. 14B is a partial cross-sectional view taken along line 14-14′ ofFIG. 12 illustrating a second alternative arrangement of the outsiderearview mirror constructed in accordance with the second embodiment ofthe present invention;

FIG. 14C is a partial cross-sectional view taken along lines 14-14′ ofFIG. 12 illustrating a third alternative arrangement of the outsiderearview mirror constructed in accordance with the second embodiment ofthe present invention;

FIG. 14D is a partial cross-sectional view taken along lines 14-14′ ofFIG. 12 illustrating a fourth alternative arrangement of the outsiderearview mirror constructed in accordance with another embodiment of thepresent invention;

FIG. 15 is a pictorial representation of two vehicles, one of whichincludes the signal mirror of the present invention;

FIG. 16 is a front elevational view of an automatic rearview mirrorembodying the information display area of another embodiment of thepresent invention;

FIG. 17 is an enlarged cross-sectional view, with portions broken awayfor clarity of illustration, of the automatic rearview mirrorillustrated in FIG. 16;

FIG. 18 is a front elevational view of the information display area,with portions broken away for clarity of illustration, of the automaticrearview mirror illustrated in FIG. 16;

FIG. 19 is a perspective view of a signal light assembly for use withanother embodiment of the present invention;

FIG. 20 is a front elevational view of an outside rearview mirrorassembly constructed in accordance with another embodiment of thepresent invention;

FIG. 21 is a partial cross-sectional view of the rearview mirrorassembly shown in FIG. 20 taken along line 21-21′;

FIG. 22 is a perspective view of an exterior portion of an exemplaryvehicle embodying the outside rearview mirror of the present inventionas illustrated in FIGS. 20 and 21;

FIG. 23A is a front perspective view of a mask bearing indicia inaccordance with another aspect of the present invention;

FIG. 23B is a front perspective view of a rearview mirror constructed inaccordance with another aspect of the present invention;

FIG. 24 is a front perspective view of a circuit board containing aplurality of light sources arranged in a configuration useful as adisplay in accordance with one aspect of the present invention;

FIG. 25 is a cross-sectional view of a display and mirror constructed inaccordance with one aspect of the present invention;

FIG. 26 is an electrical circuit diagram in block and schematic form ofan inventive circuit for controlling the contrast ratio of a displayassociated with an electrochromic mirror;

FIG. 27 is a block diagram of a display assembly for use in the presentinvention; and

FIG. 28 is a graph showing plots of the emission spectra of red andgreen LEDs and the spectral percentage transmittance of a conventionalelectrochromic mirror in a darkened state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows a front elevational view schematically illustrating aninside mirror assembly 110 and two outside rearview mirror assemblies111 a and 111 b for the driver-side and passenger-side, respectively,all of which are adapted to be installed on a motor vehicle in aconventional manner and where the mirrors face the rear of the vehicleand can be viewed by the driver of the vehicle to provide a rearwardview. Inside mirror assembly 110 and outside rearview mirror assemblies111 a and 111 b may incorporate light-sensing electronic circuitry ofthe type illustrated and described in the above-referenced CanadianPatent No. 1,300,945, U.S. Pat. No. 5,204,778, or U.S. Pat. No.5,451,822, and other circuits capable of sensing glare and ambient lightand supplying a drive voltage to the electrochromic element. Mirrorassemblies 110, 111 a, and 111 b are essentially identical in that likenumbers identify components of the inside and outside mirrors. Thesecomponents may be slightly different in configuration, but function insubstantially the same manner and obtain substantially the same resultsas similarly numbered components. For example, the shape of the frontglass element of inside mirror 110 is generally longer and narrower thanoutside mirrors 111 a and 111 b. There are also some differentperformance standards placed on inside mirror 110 compared with outsidemirrors 111 a and 111 b. For example, inside mirror 110 generally, whenfully cleared, should have a reflectance value of about 70 percent toabout 85 percent or higher, whereas the outside mirrors often have areflectance of about 50 percent to about 65 percent. Also, in the UnitedStates (as supplied by the automobile manufacturers), the passenger-sidemirror 111 b typically has a spherically bent or convex shape, whereasthe driver-side mirror 111 a and inside mirror 110 presently must beflat. In Europe, the driver-side mirror 111 a is commonly flat oraspheric, whereas the passenger-side mirror 111 b has a convex shape. InJapan, both outside mirrors have a convex shape. The followingdescription is generally applicable to all mirror assemblies of thepresent invention.

FIG. 3 shows a cross-sectional view of mirror assembly 110 having afront transparent element 112 having a front surface 112 a and a rearsurface 112 b, and a rear element 114 having a front surface 114 a and arear surface 114 b. For clarity of description of such a structure, thefollowing designations will be used hereinafter. The front surface 112 aof the front glass element will be referred to as the first surface, andthe back surface 112 b of the front glass element as the second surface.The front surface 114 a of the rear glass element will be referred to asthe third surface, and the back surface 114 b of the rear glass elementas the fourth surface. A chamber 125 is defined by a layer oftransparent conductor 128 (carried on second surface 112 b), areflector/electrode 120 (disposed on third surface 114 a), and an innercircumferential wall 132 of sealing member 116. An electrochromic medium126 is contained within chamber 125.

As broadly used and described herein, the reference to an electrode orlayer as being “carried” on a surface of an element, refers to bothelectrodes or layers that are disposed directly on the surface of anelement or disposed on another coating, layer or layers that aredisposed directly on the surface of the element.

Front transparent element 112 may be any material which is transparentand has sufficient strength to be able to operate in the conditions,e.g., varying temperatures and pressures, commonly found in theautomotive environment. Front element 112 may comprise any type ofborosilicate glass, soda lime glass, float glass, or any other material,such as, for example, a polymer or plastic, that is transparent in thevisible region of the electromagnetic spectrum. Front element 112 ispreferably a sheet of glass. The rear element must meet the operationalconditions outlined above, except that it does not need to betransparent in all applications, and therefore may comprise polymers,metals, glass, ceramics, and preferably is a sheet of glass.

The coatings of the third surface 114 a are sealably bonded to thecoatings on the second surface 112 b in a spaced-apart and parallelrelationship by a seal member 116 disposed near the outer perimeter ofboth second surface 112 b and third surface 114 a. Seal member 116 maybe any material that is capable of adhesively bonding the coatings onthe second surface 112 b to the coatings on the third surface 114 a toseal the perimeter such that electrochromic material 126 does not leakfrom chamber 125. Optionally, the layer of transparent conductivecoating 128 and the layer of reflector/electrode 120 may be removed overa portion where the seal member is disposed (not the entire portion,otherwise the drive potential could not be applied to the two coatings).In such a case, seal member 116 must bond well to glass.

The performance requirements for a perimeter seal member 116 used in anelectrochromic device are similar to those for a perimeter seal used ina liquid crystal device (LCD), which are well known in the art. The sealmust have good adhesion to glass, metals and metal oxides; must have lowpermeabilities for oxygen, moisture vapor, and other detrimental vaporsand gases; and must not interact with or poison the electrochromic orliquid crystal material it is meant to contain and protect. Theperimeter seal can be applied by means commonly used in the LCDindustry, such as by silk-screening or dispensing. Totally hermeticseals, such as those made with glass frit or solder glass, can be used,but the high temperatures involved in processing (usually near 450° C.)this type of seal can cause numerous problems, such as glass substratewarpage, changes in the properties of transparent conductive electrode,and oxidation or degradation of the reflector. Because of their lowerprocessing temperatures, thermoplastic, thermosetting or UV curingorganic sealing resins are preferred. Such organic resin sealing systemsfor LCDs are described in U.S. Pat. Nos. 4,297,401, 4,418,102,4,695,490, 5,596,023, and 5,596,024. Because of their excellent adhesionto glass, low oxygen permeability and good solvent resistance,epoxy-based organic sealing resins are preferred. These epoxy resinseals may be UV curing, such as described in U.S. Pat. No. 4,297,401, orthermally curing, such as with mixtures of liquid epoxy resin withliquid polyamide resin or dicyandiamide, or they can be homopolymerized.The epoxy resin may contain fillers or thickeners to reduce flow andshrinkage such as fumed silica, silica, mica, clay, calcium carbonate,alumina, etc., and/or pigments to add color. Fillers pretreated withhydrophobic or silane surface treatments are preferred. Cured resincrosslink density can be controlled by use of mixtures ofmono-functional, di-functional, and multi-functional epoxy resins andcuring agents. Additives such as silanes or titanates can be used toimprove the seal's hydrolytic stability, and spacers such as glass beadsor rods can be used to control final seal thickness and substratespacing. Suitable epoxy resins for use in a perimeter seal member 116include, but are not limited to: “EPON RESIN” 813, 825, 826, 828, 830,834, 862, 1001F, 1002F, 2012, DPS-155, 164, 1031, 1074, 58005, 58006,58034, 58901, 871, 872, and DPL-862 available from Shell Chemical Co.,Houston, Tex.; “ARALITE” GY 6010, GY 6020, CY 9579, GT 7071, XU 248, EPN1139, EPN 1138, PY 307, ECN 1235, ECN 1273, ECN 1280, MT 0163, MY 720,MY 0500, MY 0510, and PT 810 available from Ciba Geigy, Hawthorne, N.Y.;and “D.E.R.” 331, 317, 361, 383, 661, 662, 667, 732, 736, “D.E.N.” 431,438, 439 and 444 available from Dow Chemical Co., Midland, Mich.Suitable epoxy curing agents include V-15, V-25, and V-40 polyamidesfrom Shell Chemical Co.; “AJICURE” PN-23, PN-34, and VDH available fromAjinomoto Co., Tokyo, Japan; “CUREZOL” AMZ, 2MZ, 2E4MZ, C11Z, C 17Z,2PZ, 21Z, and 2P4MZ available from Shikoku Fine Chemicals, Tokyo, Japan;“ERISYS” DDA or DDA accelerated with U-405, 24EMI, U-410, and U-415available from CVC Specialty Chemicals, Maple Shade, N.J.; and “AMICURE”PACM, 352, CG, CG-325, and CG-1200 available from Air Products,Allentown, Pa. Suitable fillers include fumed silica such as “CAB-O-SIL”L-90, LM-130, LM-5, PTG, M-5, MS-7, MS-55, TS-720, HS-5, and EH-5available from Cabot Corporation, Tuscola, Ill.; “AEROSIL” R972, R974,R805, R812, R812 S, R202, US204, and US206 available from Degussa,Akron, Ohio. Suitable clay fillers include BUCA, CATALPO, ASP NC,SATINTONE 5, SATINTONE SP-33, TRANSLINK 37, TRANSLINK 77, TRANSLINK 445,and TRANSLINK 555 available from Engelhard Corporation, Edison, N.J.Suitable silica fillers are SILCRON G-130, G-300, G-100-T, and G-100available from SCM Chemicals, Baltimore, Md. Suitable silane couplingagents to improve the seal's hydrolytic stability are Z-6020, Z-6030,Z-6032, Z-6040, Z-6075, and Z-6076 available from Dow CorningCorporation, Midland, Mich. Suitable precision glass microbead spacersare available in an assortment of sizes from Duke Scientific, Palo Alto,Calif.

The layer of a transparent electrically conductive material 128 isdeposited on the second surface 112 b to act as an electrode.Transparent conductive material 128 may be any material which bonds wellto front element 112, is resistant to corrosion to any materials withinthe electrochromic device, resistant to corrosion by the atmosphere, hasminimal diffuse or specular reflectance, high light transmission, nearneutral coloration, and good electrical conductance. Transparentconductive material 128 may be fluorine-doped tin oxide, doped zincoxide, indium zinc oxide (Zn₃In₂O₆), indium tin oxide (ITO),ITO/metal/ITO (IMI) as disclosed in “Transparent ConductiveMultilayer-Systems for FPD Applications,” by J. Stollenwerk, B. Ocker,K. H. Kretschmer of LEYBOLD AG, Alzenau, Germany, the materialsdescribed in above-referenced U.S. Pat. No. 5,202,787, such as TEC 20 orTEC 15, available from Libbey Owens-Ford Co. of Toledo, Ohio, or othertransparent conductors. Generally, the conductance of transparentconductive material 128 will depend on its thickness and composition.IMI generally has superior conductivity compared with the othermaterials. IMI is, however, known to undergo more rapid environmentaldegradation and suffer from interlayer delamination. The thickness ofthe various layers in the IMI structure may vary, but generally thethickness of the first ITO layer ranges from about 10 Å to about 200 Å,the metal ranges from about 10 Å to about 200 Å, and the second layer ofITO ranges from about 10 Å to about 200 Å. If desired, an optional layeror layers of a color suppression material 130 may be deposited betweentransparent conductive material 128 and the second surface 112 b tosuppress the reflection of any unwanted portions of the electromagneticspectrum.

In accordance with the present invention, a combinationreflector/electrode 120 is disposed on third surface 114 a.Reflector/electrode 120 comprises at least one layer of a reflectivematerial 121 which serves as a mirror reflectance layer and also formsan integral electrode in contact with and in a chemically andelectrochemically stable relationship with any constituents in anelectrochromic medium. As stated above, the conventional method ofbuilding electrochromic devices was to incorporate a transparentconductive material on the third surface as an electrode, and place areflector on the fourth surface. By combining the “reflector” and“electrode” and placing both on the third surface, several unexpectedadvantages arise which not only make the device manufacture lesscomplex, but also allow the device to operate with higher performance.The following will outline the exemplary advantages of the combinedreflector/electrode of the present invention.

First, the combined reflector/electrode 120 on the third surfacegenerally has higher conductance than a conventional transparentelectrode and previously used reflector/electrodes, which will allowgreater design flexibility. One can either change the composition of thetransparent conductive electrode on the second surface to one that haslower conductance (being cheaper and easier to produce and manufacture)while maintaining coloration speeds similar to that obtainable with afourth surface reflector device, while at the same time decreasingsubstantially the overall cost and time to produce the electrochromicdevice. If, however, performance of a particular design is of utmostimportance, a moderate to high conductance transparent electrode can beused on the second surface, such as, for example, ITO, IMI, etc. Thecombination of a high conductance (i.e., less than 250 Ω/Y, preferablyless than 15 Ω/Y) reflector/electrode on the third surface and a highconductance transparent electrode on the second surface will not onlyproduce an electrochromic device with more even overall coloration, butwill also allow for increased speed of coloration and clearing.Furthermore, in fourth surface reflector mirror assemblies there are twotransparent electrodes with relatively low conductance, and inpreviously used third surface reflector mirrors there is a transparentelectrode and a reflector/electrode with relatively low conductance and,as such, a long buss bar on the front and rear element to bring currentin and out is necessary to ensure adequate coloring speed. The thirdsurface reflector/electrode of the present invention has a higherconductance and therefore has a very even voltage or potentialdistribution across the conductive surface, even with a small orirregular contact area. Thus, the present invention provides greaterdesign flexibility by allowing the electrical contact for the thirdsurface electrode to be very small while still maintaining adequatecoloring speed.

Second, a third surface reflector/electrode helps improve the imagebeing viewed through the mirror. FIG. 1 shows how light travels througha conventional fourth surface reflector device. In the fourth surfacereflector, the light travels through: the first glass element, thetransparent conductive electrode on the second surface, theelectrochromic media, the transparent conductive electrode on the thirdsurface, and the second glass element, before being reflected by thefourth surface reflector. Both transparent conductive electrodes exhibithighly specular transmittance but also possess diffuse transmittance andreflective components, whereas the reflective layer utilized in anyelectrochromic mirror is chosen primarily for its specular reflectance.By diffuse reflectance or transmittance component, we mean a materialwhich reflects or transmits a portion of any light impinging on itaccording to Lambert's law whereby the light rays are spread-about orscattered. By specular reflectance or transmittance component, we mean amaterial which reflects or transmits light impinging on it according toSnell's laws of reflection or refraction. In practical terms, diffusereflectors and transmitters tend to slightly blur images, whereasspecular reflectors show a crisp, clear image. Therefore, lighttraveling through a mirror having a device with a fourth surfacereflector has two partial diffuse reflectors (on the second and thirdsurface) which tend to blur the image, and a device with a third surfacereflector/electrode of the present invention only has one diffusereflector (on the second surface).

Additionally, because the transparent electrodes act as partial diffusetransmitters, and the farther away the diffuse transmitter is from thereflecting surface the more severe the blurring becomes, a mirror with afourth surface reflector appears significantly more hazy than a mirrorwith a third surface reflector. For example, in the fourth surfacereflector shown in FIG. 1, the diffuse transmitter on the second surfaceis separated from the reflector by the electrochromic material, thesecond conductive electrode, and the second glass element. The diffusetransmitter on the third surface is separated from the reflector by thesecond glass element. By incorporating a combined reflector/electrode onthe third surface in accordance with the present invention, one of thediffuse transmitters is removed, and the distance between the reflectorand the remaining diffuse transmitter is closer by the thickness of therear glass element. Therefore, the third surface metalreflector/electrode of the present invention provides an electrochromicmirror with a superior viewing image.

Finally, a third surface metal reflector/electrode improves the abilityto reduce double imaging in an electrochromic mirror. As stated above,there are several interfaces where reflections can occur. Some of thesereflections can be significantly reduced with color suppression oranti-reflective coatings; however, the most significant “double imaging”reflections are caused by misalignment of the first surface and thesurface containing the reflector, and the most reproducible way ofminimizing the impact of this reflection is by ensuring both glasselements are parallel. Presently, convex glass is often used for thepassenger side outside mirror and aspheric glass is sometimes used forthe driver side outside mirror to increase the field of view and reducepotential blind spots. However, it is difficult to reproducibly bendsuccessive elements of glass having identical radii of curvature.Therefore, when building an electrochromic mirror, the front glasselement and the rear glass element may not be perfectly parallel (do nothave identical radii of curvature), and therefore, the otherwisecontrolled double imaging problems become much more pronounced. Byincorporating a combined reflector electrode on the third surface of thedevice in accordance with the present invention, light does not have totravel through the rear glass element before being reflected, and anydouble imaging that occurs from the elements being out of parallel willbe significantly reduced.

It is desirable in the construction of outside rearview mirrors toincorporate thinner glass in order to decrease the overall weight of themirror so that the mechanisms used to manipulate the orientation of themirror are not overloaded. Decreasing the weight of the device alsoimproves the dynamic stability of the mirror assembly when exposed tovibrations. Alternatively, decreasing the weight of the mirror elementmay permit more electronic circuitry to be provided in the mirrorhousing without increasing the weight of the mirror housing. Heretofore,no electrochromic mirrors incorporating a solution-phase electrochromicmedium and two thin glass elements have been commercially available,because thin glass suffers from being flexible and prone to warpage orbreakage, especially when exposed to extreme environments. This problemis substantially improved by using an improved electrochromic deviceincorporating two thin glass elements having an improved gel material.This improved device is disclosed in commonly assigned U.S. Pat. No.5,940,201 entitled “AN ELECTROCHROMIC MIRROR WITH TWO THIN GLASSELEMENTS AND A GELLED ELECTROCHROMIC MEDIUM,” filed on or about Apr. 2,1997. The entire disclosure, including the references contained therein,of this patent is incorporated herein by reference. The addition of thecombined reflector/electrode onto the third surface of the devicefurther helps remove any residual double imaging resulting from the twoglass elements being out of parallel. Thus, in accordance with thepresent invention, chamber 124 contains a free-standing gel thatcooperatively interacts with thin glass elements 112 and 114 to producea mirror that acts as one thick unitary member rather than two thinglass elements held together only by a seal member. In free-standinggels, which contain a solution and a cross-linked polymer matrix, thesolution is interspersed in a polymer matrix and continues to functionas a solution. Also, at least one solution-phase electrochromic materialis in solution in the solvent and therefore as part of the solution isinterspersed in the polymer matrix (this generally being referred to as“gelled electrochromic medium” 126). This allows one to construct arearview mirror with thinner glass in order to decrease the overallweight of the mirror while maintaining sufficient structural integrityso that the mirror will survive the extreme conditions common to theautomobile environment. This also helps maintain uniform spacing betweenthe thin glass elements which improves uniformity in the appearance(e.g., coloration) of the mirror. This structural integrity resultsbecause the free-standing gel, the first glass element 112, and thesecond glass element 114, which individually have insufficient strengthcharacteristics to work effectively in an electrochromic mirror, couplein such a manner that they no longer move independently but act as onethick unitary member. This stability includes, but is not limited to,resistance to, flexing, warping, bowing and breaking, as well asimproved image quality of the reflected image, e.g., less distortion,double image, color uniformity, and independent vibration of each glasselement. However, while it is important to couple the front and rearglass elements, it is equally important (if not more so) to ensure thatthe electrochromic mirror functions properly. The free-standing gel mustbond to the electrode layers (including the reflector/electrode if themirror has a third surface reflector) on the walls of such a device, butnot interfere with the electron transfer between the electrode layersand the electrochromic material(s) disposed in the chamber 116. Further,the gel must not shrink, craze, or weep over time such that the gelitself causes poor image quality. Ensuring that the free-standing gelbonds well enough to the electrode layers to couple the front and rearglass elements and does not deteriorate over time, while allowing theelectrochromic reactions to take place as though they were in solution,is an important aspect of the present invention.

To perform adequately, a mirror must accurately represent the reflectedimage, and this cannot be accomplished when the glass elements (to whichthe reflector is attached) tend to bend or bow while the driver isviewing the reflected image. The bending or bowing occurs mainly due topressure points exerted by the mirror mounting and adjusting mechanismsand by differences in the coefficients of thermal expansion of thevarious components that are used to house the exterior mirror element.These components include a carrier plate used to attach the mirrorelement to the mechanism used to manipulate or adjust the position ofthe mirror (bonded to the mirror by an adhesive), a bezel, and ahousing. Many mirrors also typically have a potting material as asecondary seal. Each of these components, materials, and adhesives havevarying coefficients of thermal expansion that will expand and shrink tovarying degrees during heating and cooling and will exert stress on theglass elements 112 and 114. On very large mirrors, hydrostatic pressurebecomes a concern and may lead to double imaging problems when the frontand rear glass elements bow out at the bottom and bow in at the top ofthe mirror. By coupling the front and rear glass elements the thinglass/free-standing gel/thin glass combination act as one thick unitarymember (while still allowing proper operation of the electrochromicmirror) and thereby reduce or eliminate the bending, bowing, flexing,double image, and distortion problems and non-uniform coloring of theelectrochromic medium.

The cooperative interaction between the free-standing gel and the thinglass elements of the present invention also improves the safety aspectsof the electrochromic mirror 110 having thin glass elements. In additionto being more flexible, thin glass is more prone to breakage than thickglass. By coupling the free-standing gel with the thin glass, theoverall strength is improved (as discussed above) and further restrictsshattering and scattering and eases clean-up in the case of breakage ofthe device.

The improved cross-linked polymer matrix used in the present inventionis disclosed in commonly assigned U.S. Pat. No. 5,928,572 entitled“ELECTROCHROMIC LAYER AND DEVICES COMPRISING SAME” filed on Mar. 15,1996, and the International patent application filed on or about Mar.15, 1997, and claiming priority to this U.S. patent. The entiredisclosures of these two applications, including the referencescontained therein, are hereby incorporated herein by reference.

Generally, the polymer matrix results from crosslinking polymer chains,where the polymer chains are formed by the vinyl polymerization of amonomer having the general formula:

where R1 is optional and may be selected from the group consisting of:alkyl, cycloalkyl, poly-cycloalkyl, heterocycloalkyl, carboxyl and alkyland alkenyl derivatives thereof, alkenyl, cycloalkenyl, cycloalkadienyl,poly-cycloalkadienyl, aryl and alkyl and alkenyl derivatives thereof,hydroxyalkyl; hydroxyalkenyl; alkoxyalkyl; and alkoxyalkenyl where eachof the compounds has from 1 to 20 carbon atoms. R2 is optional and maybe selected from the group consisting of alkyl, cycloalkyl, alkoxyalkyl,carboxyl, phenyl, and keto where each of the compounds has from 1 to 8carbon atoms; and oxygen. R3, R4, and R5 may be the same or differentand may be selected from the group consisting of: hydrogen, alkyl,cycloalkyl, poly-cycloalkyl, heterocycloalkyl, and alkyl and alkenylderivatives thereof; alkenyl, cycloalkenyl, cycloalkadienyl,poly-cycloalkadienyl, aryl, and alkyl and alkenyl derivatives thereof;hydroxyalkyl; hydroxyalkenyl; alkoxyalkyl; alkoxyalkenyl; keto;acetoacetyl; vinyl ether and combinations thereof, where each of thecompounds has from 1 to 8 carbon atoms. Finally, B may be selected fromthe group consisting of hydroxyl; cyanato; isocyanato; isothiocyanato;epoxide; silanes; ketenes; acetoacetyl, keto, carboxylate, imino, amine,aldehyde and vinyl ether. However, as will be understood by thoseskilled in the art, if B is an cyanato, isocyanato, isothiocyanato, oraldehyde, it is generally preferred that R1, R2, R3, R4, and R5 not havea hydroxyl functionality.

Preferred among the monomers is methyl methacrylate; methyl acrylate;isocyanatoethyl methacrylate; 2-isocyanatoethyl acrylate; 2-hydroxyethylmethacrylate; 2-hydroxyethyl acrylate; 3-hydroxypropyl methacrylate;glycidyl methacrylate; 4-vinylphenol; acetoacetoxy methacrylate andacetoacetoxy acrylate.

Electrochromic devices are sensitive to impurities, which are shownthrough poor cycle life, residual color of the electrochromic materialin its bleached state, and poor UV stability. Although many commercialprecursors are fairly pure and perform adequately as ordered,purification would improve their performance. They can not, however, bereadily purified by distillation because their low vapor pressure makeseven vacuum distillation difficult or impossible. On the other hand, themonomers used to make the polymer matrix can be purified and thus are asignificant advance in ensuring proper performance of an electrochromicdevice. This purification may be through chromatography, distillation,recrystalization or other purification techniques well known in the art.

The monomers of the preferred embodiment of the present invention shouldalso preferably be capable of pre-polymerization, typically in thesolvent utilized in the final electrochromic mirror. Bypre-polymerization, we mean that the monomers and/or precursors reactwith one another to produce relatively long and relatively linearpolymers. These polymer chains will remain dissolved in the solvent andcan have molecular weights ranging from about 1,000 to about 300,000,although those skilled in the art will understand that molecular weightsof up to 3,000,000 are possible under certain conditions.

It should be understood that more than one monomer may bepre-polymerized together. Equation [1] shows the general formula for themonomers of the preferred embodiment of the present invention.Generally, any of the combinations of the monomers shown may be combinedinto one or more polymers (i.e., a polymer, a copolymer, terpolymer,etc.) in the pre-polymerization process. For example, one monomer may bepolymerized to give a homogeneous polymer material such as poly(2-hydroxyethyl methacrylate), poly (2-isocyanatoethyl methacrylate),and the like. However, it is generally preferred that a species with acrosslinking reactive component (e.g., hydroxyl, acetoacetyl,isocyanate, thiol etc.) be combined with another species either havingthe same crosslinking reactive component or no crosslinking reactivecomponent (e.g., methyl methacrylate, methyl acrylate, etc.). If acopolymer is produced, the ratio of the monomers without and with thecrosslinking components may range from about 200:1 to about 1:200. Anexample of these copolymers includes hydroxyethyl methacrylate (HEMA)combined with methyl methacrylate (MMA) to form a copolymer. The ratioof HEMA to MMA may range form about 1:3 to about 1:50 with the preferredratio being about 1:10. The preferred crosslinker for any of thepre-polymers having a hydroxyl (or any reactive group having an activehydrogen, such as thiol, hydroxyl, acetoacetyl, urea, melamine,urethane, etc.) is an isocyanate, isothiocyanate, and the like having afunctionality greater than one. Also, 2-isocyanatoethyl methacrylate(IEMA) may be combined with MMA in the ratio of about 1:3 to about 1:50with the preferred ratio of about 1:10. Crosslinking of any of thepolymer chains containing an isocyanate can occur with any di- orpoly-functional compound containing a reactive hydrogen, such ashydroxyl, thiol, acetoacetyl, urea, melamine, urethanes, with hydroxylbeing presently preferred. These must have a functionality greater thanone and may be the same as those described hereinabove, aliphatic oraromatic compounds or, preferably, may be 4,4′-isopropylidenediphenol,4-4′(1-4 phenylenediisopropylidene) bisphenol, 4-4′(1-3phenylenediisopropylidene), or bisphenol 1,3-dihydroxy benzene. Althoughthe above description relates to copolymers, it will be understood bythose skilled in the art that more complex structures (terpolymers,etc.) may be made using the same teachings.

Finally, two copolymers may be combined such that they crosslink withone another. For example, HEMA/MMA may be combined with IEMA/MMA and thehydroxyl groups of HEMA will self-react with the isocyanate groups ofIEMA to form an open polymeric structure. It should be understood thatthe rates of crosslinking for any of the polymers described herein canbe controlled by proper selection of the reactive crosslinking speciesemployed. For example, reaction rates can be increased by using anaromatic isocyanate or an aromatic alcohol or both. Reaction rates canbe decreased, for example, by using sterically hindered isocyanates orsterically hindered alcohols or both.

It should also be noted that the rigidity of the free-standing gel canbe altered by changing the polymer molecular weight, the weight percentof the polymer, and the crosslink density of the polymer matrix. The gelrigidity generally increases with increasing polymer concentration(weight percent), increasing crosslink density, and to some extent withincreasing molecular weight.

Typically, electrochromic mirrors are made with glass elements having athickness of about 2.3 mm. The preferred thin glass elements accordingto the present invention have thicknesses of about 1.0 mm, which resultsin a weight savings of more than 50%. This decreased weight ensures thatthe mechanisms used to manipulate the orientation of the mirror,commonly referred to as carrier plates, are not overloaded and furtherprovides significant improvement in the vibrational stability of themirror.

Front transparent element 112 may be any material which is thin andtransparent and has sufficient strength to be able to operate in theconditions, e.g., varying temperatures and pressures, commonly found inthe automotive environment. Front element 112 may comprise any type ofglass, borosilicate glass, soda lime glass, float glass or any othermaterial, such as, for example, a polymer or plastic, that istransparent in the visible region of the electromagnetic spectrum. Frontelement 112 is preferably a sheet of glass with a thickness ranging from0.5 mm to about 1.8 mm, preferably from about 0.5 to 1.6 mm, morepreferably from about 0.5 to 1.5, even more preferably from about 0.8 mmto about 1.2 mm, with the presently most preferred thickness about 1.0mm. Rear element 114 must meet the operational conditions outlinedabove, except that it does not need to be transparent, and therefore maycomprise polymers, metals, glass, ceramics, and preferably is a sheet ofglass with a thickness in the same ranges as element 112.

When both glass elements are made thin, the vibrational properties of aninterior or exterior mirror improve—although the effects are moresignificant for exterior mirrors. These vibrations that result from theengine running and/or the vehicle moving affect the rearview mirror,such that the mirror essentially acts as a weight on the end of avibrating cantilever beam. This vibrating mirror causes blurring of thereflected image that is a safety concern as well as a phenomenon that isdispleasing to the driver. As the weight on the end of the cantileverbeam (i.e., the mirror element attached to the carrier plate on theoutside mirror or the mirror mount on the inside mirror) is decreased,the frequency at which the mirror vibrates increases. If the frequencyof the mirror vibration increases to around 60 Hertz, the blurring ofthe reflected image is not visually displeasing to the vehicleoccupants. Moreover, as the frequency at which the mirror vibratesincreases, the distance the mirror travels while vibrating decreasessignificantly. Thus, by decreasing the weight of the mirror element, thecomplete mirror becomes more vibrationally stable and improves theability of the driver to view what is behind the vehicle. For example,an interior mirror with two glass elements having a thickness of 1.1 mmhas a first mode horizontal frequency of about 55 Hertz whereas a mirrorwith two glass elements of 2.3 mm has a first mode horizontal frequencyof about 45 Hertz. This 10 Hertz difference produces a significantimprovement in how a driver views a reflected image.

In the assembly and manufacture of electrochromic devices, polymericbeads may be applied to the electrochromic mirror area on the viewingarea of the second or third surface, i.e., inboard of the perimeterseal, to temporarily maintain proper cell spacing during themanufacturing process. These beads are even more useful with deviceshaving thin glass elements because they help prevent distortion anddouble image during device manufacture and maintain a uniformelectrochromic medium thickness until gellation occurs. It is desirablethat these beads comprise a material that will dissolve in theelectrochromic medium and is benign to the electrochromic system whilebeing compatible with whatever electrochromic system is contained withinthe chamber 124 (e.g., the constituents of gelled layer). While the useof PMMA beads is known, it is not preferred because they have thefollowing disadvantages: they require a heat cycle (generally at least 2hours at 85 degrees C.) to dissolve, they do not dissolve before thepreferred gels of the present invention crosslink, they can cause lightrefracting imperfections in gelled and non-gelled electrochromicdevices, and they can cause the electrochromic medium to color and clearmore slowly near the area where beads were prior to dissolving.

In accordance with another aspect of the present invention, polymericbeads, that dissolve within an electrochromic device at ambient ornear-ambient temperatures without imparting refractive imperfections,are placed or sprinkled on the second or third surface within theviewing area of the mirror or a window so that they prevent distortionand maintain cell spacing during manufacturing and dissolve very soonthereafter.

The polymeric beads can be incorporated into an electrochromic mirror asfollows: the perimeter sealing resin is charged with glass beads of theappropriate size desired for the final cell gap (typically around 135microns in diameter for a solution-phase inside electrochromic mirror)at a level of about ½ weight percent. Dry polymeric beads that are sizedabout 10% larger than the glass beads are loaded into a “salt shaker”type container with holes on one end. The rear glass element 114 is laidflat with the inside electrode surface (third surface) facing up.Plastic beads are sprinkled onto the coating (120) disposed on the thirdsurface 114 a using the salt shaker to a concentration of about 5 to 10beads per square centimeter. The perimeter sealing member 116 is appliedaround the edges of the surface of the transparent conductive electrodeon the rear surface of the front element 112 by dispensing or silkscreening as is typical for the manufacture of LCDs, such that sealmaterial covers the entire perimeter except for a gap of about 2 mmalong one edge. This gap in the seal will be used as a fill port (notshown) to introduce the electrochromic medium after assembly of theglass plates and curing of the seal. After seal application, the glassplates are assembled together by laying the first glass plate on top ofthe second glass plate and the assembly is pressed until the gap betweenthe glass plates is determined by the glass and plastic spacers. Thesealing member 116 is then cured. The electrochromic cell is then placedfill port down in an empty container or trough in a vacuum vessel andevacuated. Electrochromic fluid media is introduced into the trough orcontainer such that the fill port is submerged. The vacuum vessel isthen backfilled, which forces the fluid electrochromic material throughthe fill port and into the chamber. The fill port is then plugged withan adhesive, typically a UV light curing adhesive, and the plug materialis cured. This vacuum filling and plugging process is commonly used inthe LCD industry. If the proper polymeric bead material is used, thebeads will dissolve in the electrochromic medium without leaving a traceat room temperature or by applying moderate heat as the electrochromicmedium gels, thereby permanently fixing the cell gap.

Generally, these polymeric beads comprise a material that will readilydissolve in organic solvents, such as, for example, propylene carbonate,at ambient or near-ambient temperatures. The materials should dissolvein the electrochromic medium either within the time it takes thefree-standing gel to crosslink (which generally takes around 24 hours),but not so fast that they do not provide a spacer function duringprocessing (e.g., sealing and vacuum backfilling) of the mirror element.Materials that meet the above requirements include the followingcopolymers available from ICI Acrylics, Wilmington, Del.: “ELVACITE”2008, a MMA/methacrylic acid copolymer, “ELVACITE” 2010, aMMA/ethylacrylate copolymer, “ELVACITE” 2013, and a MMA/n-butylacrylatecopolymer, as well as poly(propylene carbonate), with “ELVACITE” 2013being presently preferred. In addition to these copolymers, it isbelieved that materials such as various polyacrylates and polyethers maybe suitable for the dissolvable beads.

Since the beads are used to maintain cell spacing for a short timeduring manufacture, they should preferably have a diameter equal to orslightly larger than the cell spacing of the device, which can beaccomplished by sieving through successive screens to obtain the desiredsize. Sieves of the appropriate size can be purchased from ATM,Milwaukee, Wis. If 135 micron glass beads will be loaded into thesealing resin, the preferred plastic bead size would be about 10% largeror 148 microns. To sieve plastic beads to the 148 micron range, astandard 145 micron and a standard 150 micron sieve would be required.If a tighter range is desired, custom-sized sieves could be ordered foran additional cost. The 150 micron sieve is placed on top of the 145micron sieve and the top 150 micron sieve is charged with unsizedplastic beads. The sieves are then vibrated such that beads smaller than150 microns will fall through the holes in the 150 micron sieve. Beadssmaller than 145 microns will fall through the bottom 145 micron sieve,and beads between 145 and 150 microns in size will be captured betweenthe 145 micron and the 150 micron sieves. If the beads tend to clump orstick together, effective separation can be achieved by flushing aliquid such as water through the sieve stack while vibrating the sieves.Beads wet-sieved in this manner must be thoroughly dried before use suchas by oven baking at 80° C. for 2 hours.

The addition of the combined reflector/electrode onto the third surfaceof the device further helps to remove any residual double imagingresulting from the two glass elements being out of parallel.

The most important factors for obtaining a reliable electrochromicmirror having a third surface reflector/electrode 120 are that thereflector/electrode have sufficient reflectance and that the mirrorincorporating the reflector/electrode has adequate operational life.Regarding reflectance, the automobile manufacturers prefer a reflectivemirror for the inside mirror having a reflectivity of at least 60percent, whereas the reflectivity requirements for an outside mirror areless stringent and generally must be at least 35 percent.

To produce an electrochromic mirror with 70 percent reflectance, thereflector must have a reflectance higher than 70 percent because theelectrochromic medium in front of the reflector reduces the reflectancefrom the reflector interface as compared to having the reflector in airdue to the medium having a higher index of refraction as compared toair. Also, the glass, the transparent electrode, and the electrochromicmedium even in its clear state are slightly light absorbing. Typically,if an overall reflectance of 65 percent is desired, the reflector shouldhave a reflectance of about 75 percent.

Regarding operational life, the layer or layers that comprise thereflector/electrode 120 must have adequate bond strength to theperipheral seal, the outermost layer must have good shelf life betweenthe time it is coated and the time the mirror is assembled, the layer orlayers must be resistant to atmospheric and electrical contactcorrosion, and must bond well to the glass surface or to other layersdisposed beneath it, e.g., the base or intermediate layer (122 or 123,respectively). The overall sheet resistance for the reflector/electrode120 may range from about 0.01 Ω/Y to about 100 Ω/Y and preferably rangesfrom about 0.2 Ω/Y to about 25 Ω/Y. As will be discussed in more detailbelow, improved electrical interconnections using a portion of the thirdsurface reflector/electrode as a high conductance contact or buss barfor the second surface transparent conductive electrode may be utilizedwhen the conductance of the third surface reflector/electrode is belowabout 2 Ω/Y.

Referring to FIG. 3 for one embodiment of the present invention, areflector/electrode that is made from a single layer of a reflectivesilver or silver alloy 121 is provided that is in contact with at leastone solution-phase electrochromic material. The layer of silver orsilver alloy covers the entire third surface 114 a of second element114. The reflective silver alloy means a homogeneous or non-homogeneousmixture of silver and one or more metals, or an unsaturated, saturated,or supersaturated solid solution of silver and one or more metals. Thethickness of reflective layer 121 ranges from about 50 Å to about 2000Å, and more preferably from about 200 Å to about 1000 Å. If reflectivelayer 121 is disposed directly to the glass surface, it is preferredthat the glass surface be treated by plasma discharge to improveadhesion.

Table 1 shows the relevant properties for a number of different metalsthat have been proposed for third surface reflectors as compared withthe materials suitable for the reflector/electrode 120 of the presentinvention. The only materials in Table 1 having reflectance propertiessuitable for use as a third surface reflector/electrode in contact withat least one solution-phase electrochromic material for an insideelectrochromic mirror for a motor vehicle are aluminum, silver, andsilver alloys. Aluminum performs very poorly when in contact withsolution-phase material(s) in the electrochromic medium because aluminumreacts with or is corroded by these materials. The reacted or corrodedaluminum is non-reflective and non-conductive and will typicallydissolve off, flake off, or delaminate from the glass surface. Silver ismore stable than aluminum but can fail when deposited over the entirethird surface because it does not have long shelf life and is notresistant to electrical contact corrosion when exposed to theenvironmental extremes found in the motor vehicle environment. Theseenvironmental extremes include temperatures ranging from about −40° C.to about 85° C., and humidities ranging from about 0 percent to about100 percent. Further, mirrors must survive at these temperatures andhumidities for coloration cycle lives up to 100,000 cycles. The otherprior art materials (silver/copper, chromium, stainless steel, rhodium,platinum, palladium, Inconel®, copper, or titanium) suffer from any oneof a number of deficiencies such as: very poor color neutrality(silver/copper and copper); poor reflectance (chromium, stainless steel,rhodium, molybdenum, platinum, palladium, Inconel®, and titanium); poorcleanability (chromium); or poor electrical contact stability (chromium,stainless steel and molybdenum).

When silver is alloyed with certain materials to produce a third surfacereflector/electrode, the deficiencies associated with silver metal andaluminum metal can be overcome. Suitable materials for the reflectivelayer are white gold and alloys of silver/palladium, silver/gold,silver/platinum, silver/rhodium, silver/titanium, etc. Examples of whitegold are described in the articles “White Golds: A Review of CommercialMaterial Characteristics & Alloy Design Alternatives,” Gold Bull., 1992,25 (3), pp. 94-103, by Greg Normandeau, and “White Golds: A Question ofCompromises—Conventional Material Properties Compared to AlternativeFormulations,” Gold Bull., 1994, 27 (3), pp. 70-86, by Greg Normandeauet al., the disclosures of which are incorporated herein by reference.The amount of the solute material, i.e., palladium, gold, etc., canvary. As can be seen from Table 1, the silver alloys surprisingly retainthe high reflectance and low sheet resistance properties of silver,while simultaneously improving their contact stability, shelf life, andalso increasing their window of potential stability when used aselectrodes in propylene carbonate containing 0.2 molartetraethylammonium tetrafluoroborate. The presently preferred materialsfor reflective layer 121 are silver/gold, silver/platinum, andsilver/palladium.

More typically, reflector/electrode 120 has, in addition to the layer ofa reflective alloy 121, an optional base layer 122 of a conductivemetal, metal oxide, metal nitride, or alloy deposited directly on thethird surface 114 a. There may also be an optional intermediate layer ofa conductive metal or alloy 123 disposed between the layer of reflectivematerial 121 and the base coat 122. If reflector/electrode 120 includesmore than one layer, there should not be galvanic corrosion between thetwo metals or alloys. If optional base layer 122 is deposited betweenthe reflective layer 121 and the glass element 114, it should beenvironmentally rugged, e.g., bond well to the third (glass) surface 114a and to reflective layer 121, and maintain this bond when the seal 116is bonded to the reflective layer. Base layer 122 may have a thicknessfrom about 50 Å to about 2000 Å, and more preferably from about 100 Å toabout 1000 Å. Suitable materials for the base layer 122 are chromium,stainless steel, silicon, titanium, nickel, molybdenum, chromium oxide,zinc oxide, and alloys of chromium/molybdenum/nickel, nickel/chromium,molybdenum, and nickel-based alloys (commonly referred to as Inconel®,available from Castle Metals, Chicago, Ill.). The main constituents ofInconel® are nickel which may range from 52 percent to 76 percent(Inconel® 617 and 600, respectfully), iron which may range from 1.5percent to 18.5 percent (Inconel® 617 and Inconel® 718, respectfully),and chromium which may range from 15 percent to 23 percent (Inconel® 600and Inconel® 601, respectfully). Inconel® 617 having 52 percent nickel,1.5 percent iron, 22 percent chromium, and typical “other” constituentsincluding 12.5 percent cobalt, 9.0 percent molybdenum, and 1.2 percentaluminum was used in the present examples.

In some instances it is desirable to provide an optional intermediatelayer 123 between the reflective layer 121 and the base layer 122 incase the material of layer 121 does not adhere well to the material oflayer 122 or there are any adverse interactions between the materials,e.g., galvanic corrosion. If used, intermediate layer 123 should exhibitenvironmental ruggedness, e.g., bond well to the base layer 122 and tothe reflective layer 121, and maintain this bond when the seal member116 is bonded to the reflective layer 121. The thickness of intermediatelayer 123 ranges from about 10 Å to about 2000 Å, and more preferablyfrom about 10 Å to about 1000 Å, and most preferably about 10 Å to about100 Å. Suitable materials for the optional intermediate layer 123 areindium, palladium, osmium, tungsten, rhenium, iridium, molybdenum,rhodium, ruthenium, stainless steel, titanium, copper, nickel, gold,platinum, and alloys whose constituents are primarily thoseaforementioned materials, such as white gold (82% Au and 18% Ni), anyother platinum group metals, and mixtures thereof. Reference is made toexamples 1 and 2 to show how the insertion of a rhodium intermediatelayer between a chromium base layer and a silver or silver alloyreflective layer increases the time to failure in copper-acceleratedacetic acid-salt spray (CASS) by a factor of 10. Example 4 shows how theinsertion of a molybdenum intermediate layer between a chromium baselayer and a silver alloy having a molybdenum flash over-coat layerincreases the time to failure in CASS by a factor of 12.

Finally, it is sometimes desirable to provide one or more optional flashover-coat layers 124 over reflective layer 121, such that it (and notthe reflective layer 121) contacts the electrochromic medium. This flashover-coat layer 124 must have stable behavior as an electrode, it musthave good shelf life, it must bond well to the reflective layer 121, andmaintain this bond when the seal member 116 is bonded thereto. It mustbe sufficiently thin, such that it does not completely block thereflectivity of reflective layer 121. In accordance with anotherembodiment of the present invention, when a very thin flash over-coat124 is placed over the highly reflecting layer, then the reflectivelayer 121 may be silver metal or a silver alloy because the flash layerprotects the reflective layer while still allowing the highly reflectinglayer 121 to contribute to the reflectivity of the mirror. In suchcases, a thin (e.g., less than about 300 Å, and more preferably lessthan about 100 Å) layer of rhodium, ruthenium, palladium, platinum,nickel, tungsten, molybdenum or their alloys, is deposited over thereflective layer 121. The thickness of the flash layer is dependent onthe material selected. For example, elements constructed with a thirdsurface coating of chrome under ruthenium under rhodium under silvercoated with a flash layer of as little as 10 Å of ruthenium showedimproved resistance compared to elements without the flash layer both tothe formation of spot defects during processing and haze in the viewingarea of the element when subjected to high temperature testing. Theinitial reflectivity of the elements with the ruthenium flash layer was70-72%. When reflective layer 121 is silver, flash layer 122 may also bea silver alloy or an aluminum-doped zinc oxide. The flash layer or athicker cover layer may also be a transparent conductor such as atransparent metal oxide.

Yet another effective reflective electrode for the third surfaceincludes a reflector layer made of silicon covered with a layer of anoxide material.

It is preferred but not essential that the third surfacereflector/electrode 120 be maintained as the cathode in the circuitrybecause this eliminates the possibility of anodic dissolution or anodiccorrosion that might occur if the reflector/electrode was used as theanode. Although as can be seen in Table 1, if certain silver alloys areused, the positive potential limit of stability extends out far enough,e.g., 1.2 V, that the silver alloy reflector/electrode could safely beused as the anode in contact with at least one solution-phaseelectrochromic material.

TABLE 1 White Light Reflectance Negative Potential Limit PositivePotential Limit Reflectance In Device Contact of Window of PotentialWindow of Potential Metal In Air (%) Stability Stability (V) Stability(V) Al >92 N/A very poor N/A N/A Cr 65 N/A poor N/A N/A Stainless 60 N/Agood N/A N/A Steel Rh 75 N/A very good N/A N/A Pt 72 N/A very good N/AN/A Inconel 55 N/A N/A N/A N/A Ag 97 84 fair −2.29 0.86 Ag2.7Pd 93 81good −2.26 0.87 Ag10Pd 80 68 good −2.05 0.97 Ag6Pt 92 80 good −1.66*0.91 Ag6Au 96 84 good −2.25 0.98 Ag25Au 94 82 good −2.3 1.2 *This numberis suspect because the test was run in propylene carbonate containingsome water.

The various layers of reflector/electrode 120 can be deposited by avariety of deposition procedures, such as RF and DC sputtering, e-beamevaporation, chemical vapor deposition, electrode position, etc., thatwill be known to those skilled in the art. The preferred alloys arepreferably deposited by sputtering (RF or DC) a target of the desiredalloy or by sputtering separate targets of the individual metals thatmake up the desired alloy, such that the metals mix during thedeposition process and the desired alloy is produced when the mixedmetals deposit and solidify on the substrate surface.

In another embodiment, the reflector/electrode 120 shown in FIG. 4 hasat least two layers (121 and 122), where at least one layer of a basematerial 122 covers substantially the entire portion of the thirdsurface 114 a and at least one layer of a reflective material 121 coversthe inner section of the third surface 114 a, but does not cover theperipheral edge portion 125 where seal member 116 is disposed.Peripheral portion 125 may be created by masking that portion of layer122 during deposition of the layer of reflective material 121, or thelayer of reflective material may be deposited over the entire thirdsurface and subsequently removed or partially removed in the peripheralportion. The masking of layer 122 may be accomplished by use of aphysical mask or through other well-known techniques, such asphotolithography and the like. Alternatively, layer 122 may be partiallyremoved in the peripheral portion by a variety of techniques, such as,for example, by etching (laser, chemical, or otherwise), mechanicalscraping, sandblasting, or otherwise. Laser etching is the presentlypreferred method because of its accuracy, speed, and control. Partialremoval is preferably accomplished by laser etching in a pattern whereenough metal is removed to allow the seal member 116 to bond directly tothe third surface 114 a while leaving enough metal in this area suchthat the conductance in this area is not significantly reduced.

In addition, an optional intermediate layer of a conductive material 123may be placed over the entire area of third surface 114 a and disposedbetween the reflective layer 121 and the base layer 122, or it may beplaced only under the area covered by layer 121, i.e., not in peripheraledge portion 125. If this optional intermediate layer is utilized, itcan cover the entire area of third surface 114 a or it may be masked orremoved from the peripheral edge portion as discussed above.

An optional flash over-coat layer 124 may be coated over the reflectivelayer 121. The reflective layer 121, the optional intermediate layer123, and the base layer 122 preferably have properties similar to thatdescribed above, except that the layer of reflective material 121 neednot bond well to the epoxy seal, since it is removed in the peripheralportion where the seal member 116 is placed. Because the interactionwith the epoxy seal is removed, silver metal itself, in addition to thealloys of silver described above, will function as the reflective layer.Alternatively, an adhesion promoter can be added to the sealing materialwhich enhances adhesion to silver or silver alloys and the reflectivelayer can be deposited over most of the third surface includingsubstantial portions under the seal area. Such adhesion promoters aredisclosed in U.S. Pat. No. 6,157,480, entitled “IMPROVED SEAL FORELECTROCHROMIC DEVICES,” the disclosure of which is incorporated hereinby reference.

Referring again to FIG. 3, chamber 125, defined by transparent conductor128 (disposed on front element rear surface 112 b), reflector/electrode120 (disposed on rear element front surface 114 a), and an innercircumferential wall 132 of sealing member 116, contains anelectrochromic medium 126. Electrochromic medium 126 is capable ofattenuating light traveling therethrough and has at least onesolution-phase electrochromic material in intimate contact withreflector/electrode 120 and at least one additional electroactivematerial that may be solution-phase, surface-confined, or one thatplates out onto a surface. However, the presently preferred media aresolution-phase redox electrochromics, such as those disclosed inabove-referenced U.S. Pat. Nos. 4,902,108, 5,128,799, 5,278,693,5,280,380, 5,282,077, 5,294,376, and 5,336,448. U.S. Pat. No. 6,020,987,entitled “AN IMPROVED ELECTROCHROMIC MEDIUM CAPABLE OF PRODUCING APRE-SELECTED COLOR,” discloses electrochromic media that are perceivedto be gray throughout their normal range of operation. The entiredisclosure of this patent is hereby incorporated herein by reference. Ifa solution-phase electrochromic medium is utilized, it may be insertedinto chamber 125 through a sealable fill port 142 through well-knowntechniques, such as vacuum backfilling and the like.

A resistive heater 138, disposed on the fourth glass surface 114 b, mayoptionally be a layer of ITO, fluorine-doped tin oxide, or may be otherheater layers or structures well known in the art. Electricallyconductive spring clips 134 a and 134 b are placed on the coated glasssheets (112 and 114) to make electrical contact with the exposed areasof the transparent conductive coating 128 (clip 134 b) and the thirdsurface reflector/electrode 120 (clip 134 a). Suitable electricalconductors (not shown) may be soldered or otherwise connected to thespring clips (134 a and 134 b) so that a desired voltage may be appliedto the device from a suitable power source.

An electrical circuit 150, such as those taught in the above-referencedCanadian Patent No. 1,300945 and U.S. Pat. Nos. 5,204,778, 5,434,407,and 5,451,822, is connected to and allows control of the potential to beapplied across reflector/electrode 120 and transparent electrode 128,such that electrochromic medium 126 will darken and thereby attenuatevarious amounts of light traveling therethrough and thus vary thereflectance of the mirror containing electrochromic medium 126.

As stated above, the low resistance of reflector/electrode 120 allowsgreater design flexibility by allowing the electrical contact for thethird surface reflector/electrode to be small while maintaining adequatecoloring speed. This flexibility extends to improving theinterconnection techniques to the layer of transparent conductivematerial 128 on the second surface 112 b. Referring now to FIGS. 5 a and5 b, an improved mechanism for applying a drive potential to the layerof transparent conductive material 128 is shown. Electrical connectionbetween the power supply and the layer of transparent conductivematerial 128 is made by connecting the buss bars (or clips 119 a) to thearea of reflector/electrode 120 a, such that the drive potential travelsthrough the area of reflector/electrode 120 a and conductive particles116 b in sealing member 116 before reaching the transparent conductor128. The reflector/electrode must not be present in area 120 c, so thatthere is no chance of current flow from reflector/electrode area 120 ato 120 b. This configuration is advantageous in that it allowsconnection to the transparent conductive material 128 nearly all the wayaround the circumference, and therefore improves the speed of dimmingand clearing of the electrochromic media 126.

In such a configuration, sealing member 116 comprises a typical sealingmaterial, e.g., epoxy 116 a, with conductive particles 116 b containedtherein. The conductive particles may be small, such as, for example,gold, silver, copper, etc., coated plastic with a diameter ranging fromabout 5 microns to about 80 microns, in which case there must be asufficient number of particles to ensure sufficient conductivity betweenthe reflector/electrode area 120 a and the transparent conductivematerial 128. Alternatively, the conductive particles may be largeenough to act as spacers, such as, for example, gold, silver, copper,etc., coated glass or plastic beads. The reflector/electrode 120 isseparated into two distinct reflector/electrode areas (120 a and 120 b,separated by an area 120 c devoid of reflector/electrode). There aremany methods of removing the reflector/electrode 120 from area 120 c,such as, for example, chemical etching, laser ablating, physical removalby scraping, etc. Deposition in area 120 c can also be avoided by use ofa mask during deposition of reflector/electrode. Sealing member 116 withparticles 116 b contacts area 120 a such that there is a conductive pathbetween reflector/electrode area 120 a and the layer of transparentconductive material 128. Thus, electrical connection to thereflector/electrode area 120 b that imparts a potential to theelectrochromic medium is connected through clips 119 b to the electroniccircuitry at reflector/electrode area 120 d (FIG. 5 b). No conductiveparticles 116 b can be placed in this reflector/electrode area 120 bbecause of the possibility of an electrical short betweenreflector/electrode area 120 b and the layer of transparent conductivematerial 128. If such an electrical short occurred, the electrochromicdevice would not operate properly. Additionally, no conductive seal 116b should be present in area 120 b.

A variety of methods can be used to ensure that no conductive particles116 b enter into this reflector/electrode area 120 b, such as, forexample, disposing a nonconductive material into the area 120 c ofreflector/electrode devoid of conductive material. A dual dispensercould be used to deposit the seal 116 with conductive particles 116 bonto reflector/electrode area 120 a and simultaneously deposit thenonconductive material into reflector/electrode area 120 c. Anothermethod would be to cure a nonconductive seal in area 120 c and thendispose a conductive material 116 c into the edge gap to electricallyinterconnect reflector/electrode area 120 a with transparent conductivelayer 128. A general method of ensuring that no conductive particlesreach reflector/electrode area 120 b is to make sure seal 116 has properflow characteristics, such that the conductive portion 116 b tends tostay behind as the sealant is squeezed out during assembly, and only thenon-conductive portion of 116 flows into area 120 b. In an alternativeembodiment, spacer member 116 need not contain conductive particles anda conductive member or material 116 c may be placed on or in the outeredge of member 116 to interconnect transparent conductive material 128to reflector/electrode area 120 a.

Yet another embodiment of an improved electrical interconnectiontechnique is illustrated in FIG. 6, where a first portion of seal member116 is applied directly onto the third surface 114 a and cured prior tothe application of reflector/electrode 120. After thereflector/electrode 120 is deposited onto the third surface 114 a overthe first portion of seal member 116, a portion of the cured seal member116 is machined off to leave 116 i as shown with a predeterminedthickness (which will vary depending on the desired cell spacing betweenthe second surface 112 b and the third surface 114 a). The cell spacingranges from about 20 microns to about 1500 microns, and preferablyranges from about 90 microns to about 750 microns. By curing the firstportion of seal member and machining it to a predetermined thickness(116 i), the need for glass beads to ensure a constant cell spacing iseliminated. Glass beads are useful to provide cell spacing, however,they provide stress points where they contact reflector/electrode 120and transparent conductor 128. By removing the glass beads, these stresspoints are also removed. During the machining, the reflector/electrode120 that is coated on first portion of seal member 116 is removed toleave an area devoid of reflector/electrode 120. A second portion ofseal member 116 ii is then deposited onto the machined area of the firstportion of seal member 116 i or on the coatings on second surface 112 bin the area corresponding to 116 i, and seal member 116 ii is curedafter assembly in a conventional manner. Finally, an outer conductiveseal member 117 may optionally be deposited on the outer peripheralportion of seal member 116 to make electrical contact between the outeredge of reflector/electrode 120 and the outer peripheral edge of thelayer of transparent conductive material 128. This configuration isadvantageous in that it allows connection to the transparent conductivematerial 128 nearly all the way around the circumference, and thereforeimproves the speed of dimming and clearing of the electrochromic media126.

Referring again to FIG. 2, rearview mirrors embodying the presentinvention preferably include a bezel 144, which extends around theentire periphery of each individual assembly 110, 111 a, and/or 111 b.The bezel 144 conceals and protects the spring clips 134 a and 134 b ofFIG. 3 (or 116 a and 116 b of FIG. 5 a; 116 i, 116 ii, and 117 of FIG.6), and the peripheral edge portions of the sealing member and both thefront and rear glass elements (112 and 114, respectively). A widevariety of bezel designs are well known in the art, such as, forexample, the bezel taught and claimed in above-referenced U.S. Pat. No.5,448,397. There are also a wide variety of housings well known in theart for attaching the mirror assembly 110 to the inside front windshieldof an automobile, or for attaching the mirror assemblies 111 a and 111 bto the outside of an automobile. A preferred mounting bracket isdisclosed in above-referenced U.S. Pat. No. 5,337,948.

The electrical circuit preferably incorporates an ambient light sensor(not shown) and a glare light sensor 160, the glare light sensor beingpositioned either behind the mirror glass and looking through a sectionof the mirror with the reflective material completely or partiallyremoved, or the glare light sensor can be positioned outside thereflective surfaces, e.g., in the bezel 144 or as described below, thesensor can be positioned behind a uniformly deposited transflectivecoating. Additionally, an area or areas of the electrode and reflector,such as 146, may be completely removed or partially removed as describedbelow to permit a vacuum fluorescent display, such as a compass, clock,or other indicia, to show through to the driver of the vehicle or asalso described below, this light emitting display assembly can be shownthrough a uniformly deposited transflective coating. The presentinvention is also applicable to a mirror which uses only one video chiplight sensor to measure both glare and ambient light and which isfurther capable of determining the direction of glare. An automaticmirror on the inside of a vehicle, constructed according to thisinvention, can also control one or both outside mirrors as slaves in anautomatic mirror system.

The following illustrative examples are not intended to limit the scopeof the present invention but to illustrate its application and use:

EXAMPLE 1

Electrochromic mirror devices incorporating a high reflectivity thirdsurface reflector/electrode were prepared by sequentially depositingapproximately 700 Å of chromium and approximately 500 Å of silver on thesurface of 2.3-mm thick sheets of flat soda lime float glass cut to anautomotive mirror element shape. A second set of high reflectivity thirdsurface reflector/electrodes were also prepared by sequentiallydepositing 700 Å of chromium and approximately 500 Å of a silver alloycontaining 3 percent by weight palladium on the glass element shapes.The deposition was accomplished by passing the glass element shapes pastseparate metal targets in a magnetron sputtering system with a basepressure of 3×10⁻⁶ torr and an argon pressure of 3×10⁻³ torr.

The chromium/silver and chromium/silver 3 percent palladium alloy coatedglass automotive mirror shapes were used as the rear planar elements ofan electrochromic mirror device. The front element was a sheet of TEC 15transparent conductor coated glass from LOF cut similar in shape andsize to the rear glass element. The front and rear elements were bondedtogether by an epoxy perimeter seal, with the conductive planar surfacesfacing each other and parallel to each other with an offset. The spacingbetween the electrodes was about 137 microns. The devices were vacuumfilled through a fill port left in the perimeter seal with anelectrochromic solution made up of:

0.028 molar 5,10-dihydro-5-10-dimethylphenazine

0.034 molar 1,1′-di(3-phenyl(n-propane))-4,4′-bipyridiniumdi(tetrafluoroborate)

0.030 molar 2-(2′-hydroxy-5′-methylphenyl)-benzotriazole

in a solution of 3 weight percent Elvacite™ 2051 polymethylmethacrylateresin dissolved in propylene carbonate.

The fill port was plugged with an UV cure adhesive, which was cured byexposure to UV light.

The devices were subjected to accelerated durability tests until theseal integrity of the device was breached or the lamination of thereflector/electrode layers or the transparent electrode layers weresubstantially degraded or dilapidated, at which time the device is saidto fail. The first test performed was steam autoclave testing in whichthe devices were sealed in a water-containing vessel and subjected to120° C. at a pressure of 15 pounds per square inch (psi). The secondtest performed was copper-accelerated acetic acid-salt spray (CASS) asdescribed in ASTM B 368-85.

When the electrochromic devices were observed after one day in testing,all of the devices failed to withstand the CASS testing, and all of thedevices failed to withstand the steam autoclave testing.

EXAMPLE 2

Other than as specifically mentioned, the devices in this example wereconstructed in accordance with the conditions and teachings inExample 1. Multilayer combination reflector/electrodes were prepared bysequentially depositing approximately 700 Å chromium, approximately 100Å rhodium, and approximately 500 Å of silver on the surface of the glasselement shapes. A second set of multilayer combinationreflector/electrodes were also prepared by sequentially depositingapproximately 700 Å of chromium, approximately 100 Å rhodium, andapproximately 500 Å of a silver alloy containing 3 percent by weightpalladium on the surface of the glass element shapes. The electrochromicdevices were constructed and tested in accordance with Example 1.

The device incorporating the sequential multilayer combination reflectorelectrode of chromium, rhodium, and silver withstood steam autoclavetesting two times longer and CASS testing 10 times longer than thedevice in Example 1 before failure occurred. The device incorporatingthe sequential multilayer combination reflector electrode of chromium,rhodium, and silver 3 percent palladium alloy withstood steam autoclavetesting three times longer and CASS testing 10 times longer than devicesin Example 1 before failure occurred.

EXAMPLE 3

Other than as specifically mentioned, the devices in this example wereconstructed in accordance with the conditions and teachings inExample 1. Multilayer combination reflector/electrodes were prepared bysequentially depositing approximately 700 Å chromium, approximately 500Å molybdenum and approximately 500 Å of a silver alloy containing 3percent by weight palladium on the surface of the glass element shapes.The electrochromic devices were constructed and tested in accordancewith Example 1.

The device incorporating the sequential multilayer combination reflectorelectrode of chromium, molybdenum, and silver 3 percent palladium alloywithstood CASS testing 10 times longer than devices in Example 1 beforefailure occurred.

EXAMPLE 4

Other than as specifically mentioned, the devices in this example wereconstructed in accordance with the conditions and teachings inExample 1. Multilayer combination reflector/electrodes were prepared bysequentially depositing approximately 700 Å chromium, approximately 500Å of a silver alloy containing 3 percent by weight palladium, andapproximately 100 Å of molybdenum on the surface of the glass elementshapes. A second set of multilayer combination reflector/electrodes werealso prepared by sequentially depositing approximately 700 Å ofchromium, approximately 500 Å molybdenum, approximately 500 Å of asilver alloy containing 3 percent by weight palladium, and approximately100 Å of molybdenum on the surface of the glass element shapes. Theelectrochromic devices were constructed and tested in accordance withExample 1.

The device incorporating the sequential multilayer combination reflectorelectrode of chromium, molybdenum, silver 3 percent palladium, andmolybdenum withstood steam autoclave testing 25 percent longer and CASStesting twelve times longer than the sequential multilayer combinationreflector electrode device of chromium, silver 3 percent palladium,molybdenum before failure occurred. Also, the device incorporating thesequential multilayer combination reflector electrode of chromium,molybdenum, silver 3 percent palladium, molybdenum withstood CASStesting three times longer than the device constructed in Example 3.Finally, the sequential multilayer combination reflector electrodedevice of chromium, silver 3 percent palladium, molybdenum withstood twotimes longer in CASS testing and twenty times longer in steam autoclavetesting than the sequential multilayer combination reflector electrodedevice of chromium, silver 3 percent palladium of Example 1.

EXAMPLE 5

Other than as specifically mentioned, the devices in this example wereconstructed in accordance with the conditions and teachings inExample 1. Multilayer combination reflector/electrodes were prepared bysequentially depositing approximately 700 Å chromium, approximately 100Å rhodium and approximately 500 Å of silver on the surface of the glasselement shapes. A second set of multilayer combinationreflector/electrodes were also prepared by sequentially depositingapproximately 700 Å of chromium, approximately 100 Å rhodium, andapproximately 500 Å of a silver alloy containing 3 percent by weightpalladium on the surface of the glass element shapes. A third set ofmultilayer combination reflector/electrodes was also prepared bysequentially depositing approximately 700 Å of chromium, approximately100 Å rhodium, and approximately 500 Å of a silver alloy containing 6percent by weight platinum on the surface of the glass element shapes. Afourth set of multilayer combination reflector/electrodes was alsoprepared by sequentially depositing approximately 700 Å of chromium,approximately 100 Å rhodium, and approximately 500 Å of a silver alloycontaining 6 percent by weight gold on the surface of the glass elementshapes. A fifth set of multilayer combination reflector/electrodes wasalso prepared by sequentially depositing approximately 700 Å ofchromium, approximately 100 Å rhodium, and approximately 500 Å of asilver alloy containing 25 percent by weight gold on the surface of theglass element shapes. The electrochromic devices were constructed inaccordance with Example 1.

Conductive clips were connected to the offset portions of the front andrear elements of the devices. A power source was connected to the clipsand 1.2 volts was applied to the devices continuously for approximately250 hours at approximately 20° C., with the connection arranged suchthat the reflector/electrode was the cathode. The device incorporatingthe sequential multilayer combination reflector electrode of chromium,rhodium, and silver exhibited a yellowing effect within theelectrochromic medium. This yellowing phenomenon was not apparent in anyof the silver alloy devices.

FIGS. 7A-7G illustrate various alternative constructions for anelectrochromic rearview mirror of the present invention, particularlywhen a light source 170, such as an information display (i.e.,compass/temperature display) or signal light, is positioned within themirror assembly behind the electrochromic mirror. According to the firstconstruction shown in FIG. 7A, the electrochromic rearview mirror wasconstructed similar to those described above, with the exception thatsecond electrode 120 includes a window 146 in the layer 121 ofreflective material in a region of second electrode 120 that is in frontof light source 170. Electrode 120 further includes a coating 172 ofelectrically conductive material that is applied over substantially allof the front surface 114 a of rear element 114. Coating 172 ispreferably at least partially transmissive so as to enable light emittedfrom light source 170 to be transmitted through the electrochromicmirror via window 146. By providing electrically conductive coating 172throughout the entire area of window 146, the electrochromic media 125in the region of window 146 will respond to the voltage applied to theclips as though window 146 was not even present. Coating 172 may be asingle layer of a transparent conductive material. Such a single layermay be made of the same materials as that of first electrode 128 (i.e.,indium tin oxide, etc.).

Transparent electrodes made of ITO, indium zinc oxide, zinc oxide,fluorine-doped tin oxide, or other transparent conductors have beenoptimized at thicknesses to maximize the transmission of visible light(typically centered around 550 nm). These transmission optimizedthicknesses are either very thin layers (<300 Å) or layers optimized atwhat is commonly called ½ wave, full wave, 1½ wave, etc. thickness. ForITO, the ½ wave thickness is about 1400 Å and the full wave thickness isaround 2800 Å. Surprisingly, these thicknesses are not optimum fortransflective (i.e., partially transmissive, partially reflective)electrodes with a single underlayer of a transparent conductor under ametal reflector such as silver or silver alloys. The optimum thicknessto achieve relative color neutrality of reflected light are centeredaround ¼ wave, ¾ wave, 1¼ wave, etc. optical thicknesses for light of500 nm wavelength. In other words the optimal optical thickness for sucha layer when underlying a metal reflector such as silver or silver alloyis mλ/4, where λ is the wavelength of light at which the layer isoptimized (e.g., 500 nm) and m is an odd integer. These optimumthicknesses are ¼ wave different from the transmission optima for thesame wavelength. Such a single layer may have a thickness of between 100Å and 3500 Å and more preferably between 200 Å and 250 Å, and a sheetresistivity of between about 3 Ω/Y and 300 Ω/Y and preferably less thanabout 100 Ω/Y.

This technique for obtaining color neutral thin metallic films is alsouseful in technologies other than electrochromics. For instance, thereis a technology described in U.S. Pat. No. 5,923,456 filed on Jul. 13,1999 and in U.S. Pat. No. 5,903,382 filed on May 11, 1999 calledReversible Electrochemical Mirror, the entire disclosures of which areincorporated herein by reference. These patents describe plating asilver film over a transparent ITO electrode covered with a very thinplatinum seed layer. Based on optical models of silver thin films withincreasing thickness (and increasing reflectivity) over a commontransmission optimized ½ wave ITO film vs. a ¼ wave ITO film, the ¼ wavesystem remains more color neutral throughout the range of thin silverfilm thickness'. As can be seen in the tables of modeled color below,the ½ wave and full wave ITO underlayer/thin silver film combinationreach a maximum b* value of approximately 32 and 19, respectively,whereas as the ¼ and ¾ wave ITO underlayer/thin silver film only reachesa maximum b* value of approximately 4 and 2.

Air/glass(n = 1.52)/XX nm ITO/1.5 nm Platinum/YY nm Silver/PropyleneCarbonate n = 1.43 Quarter wave optical thickness of ITO isapproximately 70 nm Film Color Values D65 Thicknesses illuminant 2degree observer XX YY a* b* Y 140 0 5.81 −1.92 5.26 140 5 5.22 22.2612.33 140 10 3.03 31.48 24.04 140 15 0.94 32.28 36.55 140 20 −0.65 30.1347.59 140 25 −1.68 27.17 56.44 140 30 −2.28 24.24 63.14 140 35 −2.5921.69 68.06 140 40 −2.73 19.6 71.59 140 45 −2.77 17.95 74.1 140 50 −2.7516.69 75.86 140 60 −2.68 15.01 77.95 140 70 −2.61 14.09 78.95 140 80−2.56 13.6 79.43 140 100 −2.51 13.2 79.77 280 0 9.8 −9.03 5.63 280 510.21 6.23 12.14 280 10 7.54 15.35 22.78 280 15 5.02 18.66 34.2 280 203.08 18.98 44.38 280 25 1.71 18.01 52.6 280 30 0.79 16.62 58.87 280 350.2 15.22 63.5 280 40 −0.17 13.99 66.83 280 45 −0.4 12.98 69.2 280 50−0.54 12.18 70.87 280 60 −0.67 11.09 72.86 280 70 −0.71 10.47 73.81 28080 −0.72 10.13 74.27 280 100 −0.71 9.85 74.59 70 0 −2.06 −8.75 6.73 70 50.4 −8.94 10.91 70 10 1.78 −3.83 20.03 70 15 2.68 0.12 31.09 70 20 2.772.34 41.76 70 25 2.52 3.34 50.86 70 30 2.19 3.63 58.06 70 35 1.89 3.5663.5 70 40 1.66 3.32 67.5 70 45 1.5 3.03 70.38 70 50 1.38 2.76 72.42 7060 1.26 2.3 74.86 70 70 1.21 2 76.04 70 80 1.2 1.81 76.61 70 100 1.191.64 77.01 210 0 −9.78 −1.15 6.25 210 5 −8.08 −6.8 9.84 210 10 −2.57−3.9 18.44 210 15 0.4 −0.78 29.01 210 20 1.61 1.13 39.2 210 25 1.99 2.0547.84 210 30 2.03 2.34 54.66 210 35 1.96 2.3 59.79 210 40 1.87 2.1163.54 210 45 1.8 1.87 66.23 210 50 1.75 1.62 68.14 210 60 1.7 1.21 70.41210 70 1.69 0.93 71.51 210 80 1.69 0.76 72.03 210 100 1.7 0.6 72.4

Layer 121 may be made of any of the reflective materials described aboveand is preferably made of silver or a silver alloy. The thickness ofreflective layer 121 in the arrangement shown in FIG. 7A is preferablybetween 30 Å and 800 Å. The thickness of layer 121 will depend on thedesired reflectance and transmittance properties. For an inside rearviewmirror, layer 121 preferably has a reflectance of at least 60 percentand a transmittance through window 146 of 10 to 50 percent. For anoutside mirror, the reflectance is preferably above 35 percent and thetransmittance is preferably approximately 10 to 50 percent and morepreferably at least 20 percent for those regions that are in front ofone of the lights of a signal light (as described in more detail below).

Window 146 in layer 121 may be formed by masking window area 146 duringthe application of the reflective material. At this same time, theperipheral region of the third surface may also be masked so as toprevent materials such as silver or silver alloy (when used as thereflective material) from being deposited in areas to which seal 116must adhere, so as to create a stronger bond between seal 116 andcoating 172 or element 114. Additionally, an area in front of sensor 160(FIG. 2) may also be masked. Alternatively, an adhesion promotingmaterial can be added to the seal to enhance adhesion between the sealand layer 121 as described in the above-referenced U.S. Pat. No.6,157,480.

The masking of window 146 in layer 121 may be a discrete mask such thatnone of the material of layer 121 is deposited within window area 146,or a gradient mask may be utilized, which gradually reduces the amountof the material of layer 121 from the periphery of window 146 to itscenter. The extent of the gradient masking may vary considerably suchthat virtually none of the material of layer 121 is provided over muchof the display area of window 146 with just gradient edges surroundingwindow 146 to a configuration whereby all of window 146 is covered withat least some portion of the material of layer 121.

An alternative construction to that shown in FIG. 7A is shown in FIG.7B, where electrically conductive coating 172 is formed of a pluralityof layers 174 and 176. For example, coating 172 may include a first baselayer 174 applied directly to front surface 114 a of rear element 114,and an intermediate second layer 176 disposed on first layer 174. Firstlayer 174 and second layer 176 are preferably made of materials thathave relatively low sheet resistivity and that are at least partiallytransmissive. The materials forming layers 174 and 176 may also bepartially reflective. If the light emitting display behind the partiallytransmissive window area 146 must be viewed often in bright ambientconditions or direct sunlight, it may be desirable to keep thereflectivity of the window area to a minimum by using metals with lowreflectivity or other dark, black or transparent coatings that areelectrically conductive.

The material forming layer 174 should exhibit adequate bondingcharacteristics to glass or other materials of which rear element 114may be formed, while the material forming layer 176 should exhibitadequate properties so as to bond to the material of layer 174 andprovide a good bond between the applied layer 121 and seal 116. Thus,the material used for layer 174 is preferably a material selected fromthe group consisting essentially of: chromium,chromium-molybdenum-nickel alloys, nickel-iron-chromium alloys, silicon,tantalum, stainless steel, and titanium. In the most preferredembodiment, layer 174 is made of chromium. The material used to formsecond layer 176 is preferably a material selected from the groupconsisting essentially of, but not limited to: molybdenum, rhodium,ruthenium, nickel, tungsten, tantalum, stainless steel, gold, titanium,and alloys thereof. In the most preferred embodiment, second layer 176is formed of nickel, rhodium, ruthenium, or molybdenum. If first layer174 is formed of chromium, layer 174 preferably has a thickness ofbetween 5 Å and 50 Å. If the layer of chromium is much thicker, it willnot exhibit sufficient transmittance to allow light from a light source170, such as a display or signal light, to be transmitted through window146. The thickness of layer 176 is selected based upon the material usedso as to allow between 10 to 50 percent light transmittance through bothof layers 174 and 176. Thus, for a second layer 176 formed of eitherrhodium, ruthenium, nickel, or molybdenum, layer 176 is preferablybetween 50 Å and 150 Å. While the thicknesses of layers 174 and 176 arepreferably selected to be thin enough to provide adequate transmittance,they must also be thick enough to provide for adequate electricalconductivity so as to sufficiently clear or darken electrochromic media125 in the region of window 146. The coating 172 should thus have asheet resistivity of less than 100 Ω/Y and preferably less than 50 Ω/Yto 60 Ω/Y.

The arrangement shown in FIG. 7B provides several advantages over theconstruction shown and described with respect to FIG. 7A. Specifically,the metals used in forming coating 172 contribute to the totalreflectance of reflector electrode 120. Accordingly, the layer of thereflective material 121 need not be made as thick. If, for example,silver or a silver alloy is used to form layer 121, the layer ofthickness is between 50 Å and 150 Å, thereby eliminating some of thematerial costs in providing the reflective layer. Further, the use ofreflective metals in forming coating 172 provides for a degree ofreflectance within window 146, thereby providing a much more asceticallypleasing appearance than if window 146 were devoid of any reflectivematerial whatsoever. Ideally, coating 172 provides between 30 and 40percent reflectivity in window 146. If the reflectance in window 146 istoo high, bright light will tend to wash out the display in the sensethat it eliminates the contrast between the light of the display andlight reflecting outward from coating 172. As shown in FIG. 7B, layer121 is masked in the region of window 146. Such masking may be discreteor gradient as discussed above.

Another benefit of utilizing metals to form conductive coating 172 isthat such metals are much easier and less expensive to process thanmetal oxides, such as indium tin oxide. Such metal oxides requireapplication in oxygen-rich chambers at very high temperatures, whereasmetal layers may be deposited without special oxygen chambers and atmuch lower temperatures. Thus, the process for applying multiple metallayers consumes much less energy and is much less expensive than theprocesses for forming metal oxide layers.

A third alternate arrangement for the electrochromic mirror of thepresent invention is shown in FIG. 7C. The construction shown in FIG. 7Cis essentially the same as that shown in FIG. 7B except that a thinsilver or silver alloy layer 178 is formed on conductive coating 172within window 146. By providing only a thin layer 178 of reflectivematerial in window 146, adequate transmittance may still be providedthrough window 146 while increasing the reflectivity and electricalconductivity in that area. Layer 178 may have a thickness of between 40Å and 150 Å, whereas the layer of reflective material 121 in the otherareas may have a thickness in the order of between 200 Å and 1000 Å. Thethin layer 178 of reflective material may be formed by initially maskingthe area of window 178 while applying a portion of reflective layer 121and then removing the mask during deposition of the remainder of layer121. Conversely, a thin layer of reflective material may first bedeposited and then a mask may be applied over window 146 while theremainder of reflective layer 121 is deposited. As will be apparent tothose skilled in the art, thin layer 178 may also be formed withoutmasking by depositing reflective layer 121 to its full thickness andsubsequently removing a portion of layer 121 in the region of window146. Further still, the masking may be gradient so as to graduallyreduce the thickness of layer 121 in the region of window 146.

A modification of the configuration shown in FIG. 7C is illustrated inFIG. 7D. As will be apparent from a comparison of the drawings, theconstruction of FIG. 7D only differs from that shown in FIG. 7C in thatlayers 174 and 176 constituting conductive coating 172 are made thinner(designated as thin layers 180 and 181) in the region ofreflector/electrode 120 that is in front of light source 170. As such,thin layer 180 may have a thickness of between 5 Å and 50 Å, whereaslayer 174 may have thicknesses anywhere between 100 Å and 1000 Å.Similarly, thin layer 181 may be made of the same material as layer 176but would have a thickness of between 50 Å and 150 Å, while layer 176may have thicknesses on the order of 100 Å to 1000 Å. Thus, with theconstruction shown in FIG. 7D, the electrical conductivity,reflectivity, and transmittance within region 146 may be optimizedwithin that region while enabling the reflectance and electricalconductivity in the other regions to be optimized without concern as tothe transmittance in those areas.

FIG. 7E shows yet another alternative construction for second electrode120. In the construction shown in FIG. 7E, second electrode 120 includesan electrically conductive coating 172 and a reflective coating 178formed over the entire third surface 114 a of the mirror. By makingreflective coating 178 uniformly partially transmissive, a light source,such as a display or signal light, may be mounted in any location behindthe mirror and is not limited to positioning behind any particularwindow formed in second electrode 120. Again, for a rearview mirror,second electrode 120 preferably has a reflectance of at least 35 percentfor an outside mirror and at least 60 percent for an inside mirror and atransmittance of preferably at least 10 percent. Conductive coating 172is preferably a single layer of ITO or other transparent conductivematerials, but may also consist of one or more layers of the partiallyreflective/partially transmissive electrically conductive materialsdiscussed above.

Reflective coating 178 may be constructed using a single, relativelythin, layer of a reflective electrically conductive material such assilver, silver alloy, or the other reflective materials discussed above.If the reflective material is silver or a silver alloy, the thickness ofsuch a thin layer should be limited to about 500 Å or less, and atransparent conductive material, such as ITO or the like, should beutilized as electrically conductive layer 172, such that secondelectrode 120 may have sufficient transmittance to allow a display orsignal light to be viewed from behind the mirror. On the other hand, thethickness of the single layer of reflective material should be about 10Å or more depending upon the material used to ensure sufficientreflectivity.

To illustrate the features and advantages of an electrochromic mirrorconstructed in accordance with the embodiment shown in FIG. 7E, tenexamples are provided below. In these examples, references are made tothe spectral properties of models of electrochromic mirrors constructedin accordance with the parameters specified in each example. Indiscussing colors, it is useful to refer to the CommissionInternationale de I'Eclairage's (CIE) 1976 CIELAB Chromaticity Diagram(commonly referred to as the L*a*b* chart). The technology of color isrelatively complex, but a fairly comprehensive discussion is given by F.W. Billmeyer and M. Saltzman in Principles of Color Technology, 2ndEdition, J. Wiley and Sons Inc. (1981), and the present disclosure, asit relates to color technology and terminology, generally follows thatdiscussion. On the L*a*b* chart, L* defines lightness, a* denotes thered/green value, and b* denotes the yellow/blue value. Each of theelectrochromic media has an absorption spectra at each particularvoltage that may be converted to a three number designation, theirL*a*b* values. To calculate a set of color coordinates, such as L*a*b*values, from the spectral transmission or reflectance, two additionalitems are required. One is the spectral power distribution of the sourceor illuminant. The present disclosure uses CIE Standard Illuminant A tosimulate light from automobile headlamps and uses CIE StandardIlluminant D₆₅ to simulate daylight. The second item needed is thespectral response of the observer. The present disclosure uses the 2degree CIE standard observer. The illuminant/observer combinationgenerally used for mirrors is then represented as A/2 degree and thecombination generally used for windows is represented as D₆₅/2 degree.Many of the examples below refer to a value Y from the 1931 CIE Standardsince it corresponds more closely to the spectral reflectance than L*.The value C*, which is also described below, is equal to the square rootof (a*)²+(b*)², and hence, provides a measure for quantifying colorneutrality.

It should be noted that the optical constants of materials vary somewhatwith deposition method and conditions employed. These differences canhave a substantial effect on the actual optical values and optimumthicknesses used to attain a value for a given coating stock.

According to a first example, an electrochromic mirror was modeledhaving a back plate 114 (FIG. 7E) of glass, a layer 172 of ITO ofapproximately 2000 Å, a layer 178 of an alloy of silver containing 6percent gold (hereinafter referred to as 6Au94Ag) of approximately 350Å, an electrochromic fluid/gel layer 125 having a thickness ofapproximately 140 microns, a layer 128 of approximately 1400 Å of ITO,and a glass plate 112 of 2.1 mm. Using D65 illuminant at 20 degree angleof incidence, the model outputs were Y=70.7, a*=+1, and b*=+9.5. Thismodel also indicated a spectrally dependent transmittance that was 15percent over the blue-green region decreasing in the red color region ofthe spectrum to approximately 17 percent in the blue-green region of thespectrum. Elements were constructed using the values and the model astarget parameters for thickness, and the actual color, and reflectionvalues corresponded closely to those models with transmission values ofapproximately 15 percent in the blue and green region. In this example,1400 Å ITO (½ wave) would produce a far more yellow element (b* ofapproximately 18).

Typically, thin silver or silver alloy layers are higher in blue-greentransmission and lower in blue-green light reflection which imparts ayellow hue to the reflected image. The 2000 Å ITO underlayer ofapproximately ¾ wave in thickness supplements the reflection ofblue-green light which results in a more neutral hue in reflection.Other odd quarter wave multiples (i.e., ¼, 5/4, 7/4, etc.) are alsoeffective in reducing reflected color hue. It should be noted that othertransparent coatings, such as (F)SnO or (AL)ZnO, or a combination ofdielectric, semi-conductive, or conductive coatings, can be used tosupplement blue-green reflection and produce a more neutral reflectedhue in the same manner.

According to a second example of the embodiment illustrated in FIG. 7E,an electrochromic mirror was modeled having a back plate 114 of glass,layer 172 including a sublayer of titanium dioxide of approximately 441Å and a sublayer of ITO of 200 Å, a layer 178 of 6Au94Ag ofapproximately 337 Å, an electrochromic fluid/gel 125 having a thicknessof approximately 140 microns, a layer 128 of approximately 1400 Å ofITO, and a glass plate 112 of 2.1 mm. In air, the model of theconductive thin film 120 on glass 114 for this example, using D65illuminant at 20 degree angle of incidence, exhibited values ofapproximately Y=82.3, a*=0.3, and b*=4.11. This model also indicated arelatively broad and uniform transmittance of 10-15 percent across mostof the visible spectrum, making it an advantageous design for aninterior rearview mirror with a multi-colored display or a white lightdisplay or illuminator. When this back plate system 114, 120 isincorporated into an electrochromic mirror, the predicted overallreflectance decreases and the transmittance increases.

According to a third example of an electrochromic mirror constructed asshown in FIG. 7E, an electrochromic mirror was modeled having a backplate 114 of glass, a layer 172 including a sublayer of titanium dioxideof approximately 407 Å and a sublayer of ITO of 200 Å, a layer 178 of6Au94Ag of approximately 237 Å, an electrochromic fluid/gel layer 125having a thickness of approximately 140 microns, a layer 128 ofapproximately 1400 Å of ITO, and a glass plate 112 of 2.1 mm. In air,the model of the conductive thin film 120 on glass 114, for thisexample, using D65 illuminant at 20 degree angle of incidence, exhibitedvalues of approximately Y=68.9, a=0.03, and b=1.9. This model alsoindicated a relatively broad and uniform transmittance of approximately25 to 28 percent across most of the visible spectrum, making it anadvantageous design for an exterior rearview mirror with a multi-colordisplay or a white light display or illuminator. When this back platesystem 114, 120 is incorporated into an electrochromic mirror, thepredicted overall reflectance decreases and the transmittance increases.

According to a fourth example of the embodiment shown in FIG. 7E, anelectrochromic mirror was modeled having a back plate 114 of glass, alayer 172 including a sublayer of titanium dioxide of approximately 450Å and a sublayer of ITO of 1600 Å, a layer 178 of 6Au94Ag ofapproximately 340 Å, an electrochromic fluid/gel layer 125 having athickness of approximately 140 microns, a layer 128 of approximately1400 Å of ITO, and a glass plate 112 of 2.1 mm. In air, the model of theconductive thin film 120 on glass 114, for this example, using D65illuminant at 20 degree angle of incidence, exhibited values ofapproximately Y=80.3, a*=−3.45, and b*=5.27. This model also indicated arelative transmittance peak at about 600 nm of approximately 17 percent.When this back plate system 114, 120 is incorporated into anelectrochromic mirror, the predicted overall reflectance decreases andthe transmittance increases. As one compares this stack to the secondexample, it illustrates, in part, a principle of repeating optima in theprimarily transmissive layer or layers (e.g., layer 172) of thesedesigns as one increases their thickness or thicknesses. The optima willbe determined by several factors which will include good colorneutrality, reflection, and transmission.

According to a fifth example of the embodiment shown in FIG. 7E, anelectrochromic mirror was modeled having a back plate 114 of glass; alayer 172 including a sublayer of titanium dioxide of approximately 450Å, a sublayer of ITO of 800 Å, a sublayer of silica of 50 Å, and anadditional sublayer of ITO of 800 Å; a layer 178 of 6Au94Ag ofapproximately 340 Å; an electrochromic fluid/gel layer 125 having athickness of approximately 140 microns, a layer 128 of approximately1400 Å of ITO; and a glass plate 112 of 2.1 mm. In air, the model of theconductive thin film 120 on glass 114, for this example, using D65illuminant at 20 degree angle of incidence, exhibited values ofapproximately Y=80.63, a*=−4.31, and b*=6.44. This model also indicateda relative transmittance peak at about 600 nm of approximately 17percent. When this back plate system is incorporated into anelectrochromic mirror, the predicted overall reflectance decreases andthe transmittance increases. This stack also demonstrates, in part, aprinciple of a flash layer incorporation in these designs. In thisparticular case, the 50 Å silica layer does not contribute substantiallyto the design when compared to the fourth example, nor does it detractfrom it greatly. The insertion of such layers would not, in the opinionof the inventors, circumvent any claims that might depend on the numberof layers or the relative refractive indices of layer sets. Flash layershave been shown to impart substantial advantages when used over layer178 and are discussed above. It is also believed that such flash layerscould have adhesion promotion or corrosion resistance advantages whenpositioned between layers 172 and 178 as well as between glass 114 andlayer(s) 120, especially when comprised of metal/alloys mentioned aboveas having such functions in thicker layers.

According to a sixth example of the embodiment shown in FIG. 7E, anelectrochromic mirror was modeled having a back plate 114 of glass, alayer 172 including a sublayer of titanium dioxide of approximately 450Å and a sublayer of ITO of 1600 Å, a layer 178 of silver of 290 Å and aflash layer of 6Au94Ag of approximately 50 Å, an electrochromicfluid/gel layer 125 having a thickness of approximately 140 microns, alayer 128 of approximately 1400 Å of ITO, and a glass plate 112 of 2.1mm. In air, on glass 114, the model of the conductive thin film 120 forthis example, using D65 illuminant at 20 degree angle of incidence,exhibited values of approximately Y=81.3, a*=−3.26, and b*=4.16. Thismodel also indicated a relative transmittance peak at about 600 nm ofabout 17 percent. When this back plate system 114, 120 is incorporatedinto an electrochromic mirror, the predicted overall reflectancedecreases and the transmittance increases. As one compares this stack tothe fourth example, it illustrates, in part, the principle of using aflash layer of a silver alloy over silver. The potential advantages ofsuch a system for layer 178, as opposed to a single alloy layer per thefourth example, include, but are not limited to, reduced cost, increasedreflectivity at the same transmission or increased transmissivity at thesame reflectance, decreased sheet resistance, and the possibility ofusing a higher percentage of alloyed material in the flash overcoatlayer to maintain enhanced electrode surface properties the silver alloyexhibits over pure silver. Similar potential advantages apply to thecases of different percentage alloys or a graded percentage alloy inlayer 178.

According to a seventh example of the embodiment shown in FIG. 7E, anelectrochromic mirror was modeled having a back plate 114 of glass, alayer 172 of silicon of approximately 180 Å, a layer 178 of 6Au94Ag ofapproximately 410 Å, an electrochromic fluid/gel layer 125 having athickness of approximately 140 microns, a layer 128 of approximately1400 Å of ITO, a glass plate 112 of 2.1 mm. In air, on glass 114, themodel of the conductive thin film 120 for this example, using D65illuminant at 20 degree angle of incidence, exhibited values of Y=80.4,a=0.9, and b=−3.39. In contrast, a thin layer of 6Au94Ag on glass withsimilar reflectivity exhibits a yellow hue in reflection. The model alsoindicated a spectrally dependent transmittance that reached a peak ofabout 18 percent at 580 nm. When this back plate system 114, 120 isincorporated into an electrochromic mirror, the predicted overallreflectance and the transmittance increases. In this case, the valueswould be appropriate for an automotive interior transflective mirror.This system would be especially useful if the silicon were deposited asa semi-conductive material, thereby allowing for masking of the silveralloy layer so that the silver alloy would be deposited primarily in theviewing area while still maintaining conductivity to the area to bedarkened.

According to an eighth example of the embodiment shown in FIG. 7E, anelectrochromic rearview mirror was modeled having a back plate 114 ofglass, a layer 172 including a sublayer of silicon of approximately 111Å and a sublayer of ITO of approximately 200 Å, a layer 178 of 6Au94Agof approximately 340 Å, an electrochromic fluid/gel layer 125 having athickness of approximately 140 microns, a layer 128 of approximately1400 Å of ITO, and a glass plate 112 of 2.1 mm. In air, on glass 114,the model of the conductive thin film 120 for this example using D65illuminant at 20 degree angle of incidence exhibited values ofapproximately Y=80.7, a*=0.1, and b=−1.7. The model also indicated aspectrally dependent transmittance that reached a peak at about 18percent at 600 nm. When this back plate system 114, 120 is incorporatedinto an electrochromic mirror, the predicted overall reflectancedecreases and the transmittance increases. In this case, the valueswould be appropriate for an automotive transflective mirror. Also inthis case, masking of the silver alloy layer could take place in theseal area, and the conductivity of the back electrode of the systemwould be maintained by the ITO layer whether or not the silicon weresemi-conductive. This example is advantageous in that it utilizes thinlayers, which are easier to form during high volume manufacturing.

According to a ninth example of the embodiment shown in FIG. 7E, anelectrochromic mirror was modeled having a back plate 114 of glass, alayer 172 including a sublayer of silicon of approximately 77 Å and asublayer of ITO of approximately 200 Å, a layer 178 of 6Au94Ag ofapproximately 181 Å, an electrochromic fluid/gel layer 125 having athickness of approximately 140 microns, a layer 128 of approximately1400 Å of ITO, and a glass plate 112 of 2.1 mm. In air, on glass, themodel of the conductive thin film 120 for this example, using D65illuminant at 20 degree angle of incidence, exhibited values ofapproximately Y=64.98, a=1.73, and b=−2.69. The model also indicated aspectrally dependent transmittance that reached a peak of about 35percent at 650 nm. When this back plate system is incorporated into anelectrochromic mirror, the predicted overall reflectance decreases andthe transmittance increases. In this case, the values would beappropriate for an automotive exterior transflective mirror.

According to a tenth example of the embodiment shown in FIG. 7E, anelectrochromic mirror was modeled having a back plate 114 of glass, alayer 172 of fluorine-doped tin oxide of approximately 1957 Å (¾ waveoptima thickness), a layer 178 of 6Au94Ag of approximately 350 Å, anelectrochromic fluid/gel layer 125 having a thickness of approximately140 microns, a layer 128 of approximately 1400 Å of ITO, and a glassplate 112 of 2.1 mm. In air, on glass 114, the model of the conductivethin film 120, for this example, using D65 illuminant at 20 degree angleof incidence, exhibited outputs of approximately Y=80.38, a*=1.04, andb*=5.6. The model also indicated a spectrally dependent transmittancethat overall diminished as wavelength increased in the visible range.Transmittance at 630 nm was predicted as approximately 10 percent. Whenthis back plate system is incorporated into an electrochromic mirror,the predicted overall reflectance decreases and the transmittanceincreases. In this case, the values would be appropriate for anautomotive interior transflective mirror.

In a mirror construction, such as that shown in FIG. 7E, the mirrorpreferably exhibits a reflectivity of at least 35 percent, morepreferably at least 50 percent, and more preferably at least 65 percentfor an outside mirror and, for an inside mirror, the mirror preferablyexhibits a reflectance of at least 70 percent and more preferably atleast 80 percent. To obtain such reflectance levels, the reflectivesecond electrode 120 should have a slightly higher reflectance. Themirror preferably exhibits a transmittance of at least about 5 percent,more preferably at least about 10 percent, and most preferably at leastabout 15 percent. To obtain these transmittance levels, the secondelectrode 120 may have a slightly lower transmittance.

Because electrochromic mirrors having a b* value of greater than +15have an objectionable yellowish hue, it is preferable that the mirrorexhibits a b* value less than about 15, and more preferably less thanabout 10. Thus, second electrode 120 preferably exhibits similarproperties.

To obtain an electrochromic mirror having relative color neutrality, theC* value of the mirror should be less than 20. Preferably, the C* valueis less than 15, and more preferably is less than about 10. Secondelectrode 120 preferably exhibits similar C* values.

The inventors have recognized that, when a thin layer of silver orsilver alloy is used in a rearview mirror such as those described above,the thin layer may impart a light yellow hue (b* greater than +15) toobjects viewed in the reflection particularly when the thin layer ofsilver or silver alloy is made thin enough to impart sufficienttransmittance of 5 percent or more. This causes the mirror to no longerappear color neutral (C* greater than 20). Conversely, transmissionthrough the film is higher for blue light than for red light. The tenpreceding examples compensate for this liability by selection of theappropriate thicknesses of various underlayer films. Another approach tominimizing the yellow hue of the reflected images is to reflect thetransmitted blue light back through the mirror. Typically, in the priorart signal or display mirrors, a coating of black paint is applied tothe fourth surface of the mirror in all areas except for where a displayis mounted (if one is employed). Such a black coating was designed toabsorb any light that is transmitted through the mirror and itsreflective layer(s). To minimize the yellow hue of the reflected imageappearing when a thin silver/silver alloy material is used, the blackcoating may be replaced with a coating 182 that reflects the blue lightback through the mirror rather than absorbing such blue light.Preferably, blue paint is used in place of the black paint since theblue backing reflects blue light. Alternatively, coating 182 may bewhite, gray, or a reflective coating such as chrome, since they toowould reflect blue light back through the reflective layer(s) and theremainder of the mirror.

To demonstrate the effectiveness of blue coating 182 on the fourthsurface 114 b of a mirror, an electrochromic mirror was constructed witha thin layer of silver 178 over a 100 Ω/Y ITO layer 172 as the thirdsurface reflector/electrode 120. The white light reflectivity of themirror was about 52 percent, and the white light transmission was about30 percent. The mirror had a noticeably yellow hue in reflection and ablue hue in transmission. The mirror was placed on a black backgroundand the color was measured using a SP-68 Spectrophotometer from X-Rite,Inc. of Grandville, Mich. The measured b* value was +18.72. The samemirror was then placed on a blue background and the color was againmeasured. With the blue background, the measured b* value fell to +7.55.The mirror thus exhibited noticeably less yellow hue in reflection onthe blue background as compared to a black background.

Yet another variation of reflector/electrode 120 is illustrated in FIG.7F. As illustrated, reflector/electrode 120 is constructed acrosssubstantially the entire front surface 114 a of rear element 114 with anelectrically conductive multi-layer interferential thin-film coating190. Conductive thin-film coating 190 is preferably tailored to maximizetransmittance to light having wavelengths within a narrow bandcorresponding to the wavelength of light emitted from light source 170.Thus, if light source 170 were a signal light including red, red-orange,or amber AlGaAs or AlInGaP LEDs, the light emitted from such LEDs wouldhave wavelengths in the range of 585 nm to 660 nm, and conductivethin-film coating 190 would be tailored to maximize spectraltransmittance at those wavelengths. By increasing the transmittancepreferentially within this relatively narrow band of wavelengths, theaverage luminous reflectance to white light remains relatively high. Aswill be apparent from the four examples provided below of electrodesconstructed using such conductive thin-film coatings, the conductivethin-film coating as so constructed includes a first layer 184 of afirst material having a relatively high refractive index, a second layer186 of a second material formed on first layer 184 where the secondmaterial has a relatively low refractive index, and a third layer 187formed on second layer 186 and made of a material that has a relativelyhigh refractive index. Conductive thin-film coating 190 may also includea thin fourth layer 188 of an electrically conductive material formed onthird layer 187. If third layer 187 is not electrically conductive,fourth layer 188 of an electrically conductive material must be disposedon third layer 187. If the first, second, and third layers providesufficient reflectivity, such a fourth layer 188 may be made of atransparent conductive material. If not, fourth layer 188 may be made ofa reflective material.

Conductive thin-film coating 190 preferably exhibits: a luminousreflectance of 35 to 95 percent, a reflected C* value of 20 or less, asignal light/display luminous transmittance of 10 percent or more, and asheet resistance of less than 100 Ω/Y. More preferably, C* is less than15 and most preferably less than 10, and the value of a* is negative. Asa measure of comparison, luminous reflection and reflected C* for thiscoating may be measured using one or more of the CIE illuminants A, B,C, or D55, D65, an equal-energy white source or other broad-band sourcemeeting the SAE definition of white. Luminous reflectance and reflectedC* for this coating may be measured at one or more angles of incidencebetween 10° and 45° from the surface normal. The signal light/displayluminous transmittance for this coating may be measured using one ormore signal or display sources such as amber, orange, red-orange, red,or deep red LEDs, vacuum fluorescent displays (VFDs), or other lamps ordisplays, and at one or more angles of incidence between 20° and 55°from the surface normal. As will be apparent to those skilled in theart, “Luminous Reflectance” and “Signal light/display LuminousTransmittance” imply use of either or both of the 1931 CIE 2 degreeobserver V_(λ) or V_(λ)′ as the eye-weighting functions.

By configuring conductive thin-film coating 190 to have a reflectance,transmittance, electrical conductivity, and a reflected C* value withinthe above parameters, an electrode may thus be constructed that hasmedium to high reflectance, substantially neutral reflectance forfaithful rendering, medium to high in-band signal light/displaytransmittance for efficiency and brightness, and low sheet resistancefor good electrochromic functionality.

In the specific examples of such a conductive thin-film coating, thefirst and third materials forming first and third layers 184 and 187,respectively, may be the same or a different material selected from thegroup consisting essentially of indium tin oxide, fluorine-doped tinoxide, titanium dioxide, tin dioxide, tantalum pentoxide, zinc oxide,zirconium oxide, iron oxide, silicon, or any other material having arelatively high refractive index. Second layer 186 may be made ofsilicon dioxide, niobium oxide, magnesium fluoride, aluminum oxide, orany other material having a low refractive index. First layer 184 mayhave a thickness of between about 200 Å to 800 Å, second layer 186 mayhave a thickness of between about 400 Å to 1200 Å, third layer 187 mayhave a thickness between about 600 Å to 1400 Å, and layer 188 may have athickness of about 150 Å to 300 Å. Other optima thicknesses outsidethese ranges may also be obtainable per the above description. Insertingadditional layer sets of low and high index materials can raisereflectance further. Preferably, the electrically conductive materialforming fourth layer 188 is made of a reflective material such as silveror silver alloy, or of a transparent conductive material such as ITO.

According to a first example of conductive thin-film coating 190, anelectrochromic mirror was modeled having a front element 112 having athickness of 2.2 mm, a first electrode 128 made of ITO and having athickness of approximately 1400 Å, an electrochromic fluid/gel having athickness of approximately 137 to 190 microns, and a conductivethin-film coating 190 provided on a rear glass substrate 114. Conductivethin-film coating 190 in this first example included a first layer 184made of ITO and having a thickness of approximately 750 Å, a secondlayer 186 made of SiO₂ and having a thickness of approximately 940 Å, athird layer 187 made of ITO and having a thickness of approximately 845Å, and a fourth layer 188 made of silver and having a thickness of 275Å. In air, the conductive thin-film coating 190 modeled in this firstexample exhibited a luminous reflectance of approximately 80.2 percentfor white light and a spectral transmittance of approximately 22.5percent on average for light having wavelengths between 620 nm and 650nm. Such characteristics make the conductive thin-film coating 190according to this first example suitable for use either in an inside oroutside rearview mirror. When this conductive thin-film coating isapplied to the front surface of rear glass element and incorporated intoan electrochromic mirror, the overall reflectance decreases and thetransmittance increases.

According to a second example, another electrochromic mirror was modeledhaving the same features as discussed above with the exception thatconductive thin-film coating 190 included a first layer 184 made of ITOand having a thickness of approximately 525 Å, a second layer of SiO₂having a thickness of approximately 890 Å, a third layer 187 made of ITOand having a thickness of approximately 944 Å, and a fourth layer 188made of silver and having a thickness of approximately 168 Å. In air,the conductive thin-film coating as constructed in the second examplehas a luminous reflectance of approximately 63 percent for white lightincident thereupon at a 20° angle of incidence, and a spectraltransmittance of approximately 41 percent on average for light havingwavelengths in the 620 nm to 650 nm wavelength range at 20° angle ofincidence. Such a conductive thin-film coating 190 is particularlysuitable for an outside rearview mirror. When this conductive thin-filmcoating is applied to the front surface of rear glass element andincorporated into an electrochromic mirror, the overall reflectancedecreases and the transmittance increases.

A conductive thin-film coating according to a third example was modeledthat was made of the same materials as described for the first twoconductive thin-film coatings except that first layer 184 had athickness of approximately 525 Å, second layer 186 had a thickness ofapproximately 890 Å, third layer 187 had a thickness of approximately945 Å, and fourth layer 188 had a thickness of approximately 170 Å. Inair, the conductive thin-film coating thus modeled had a luminousreflectance of 63 percent at 20° angle of incidence for illuminationwith white light, and an average spectral transmittance of approximately41 percent for light having wavelengths between the 620 nm and 650 nmwavelength range at 20° angle of incidence. When this conductivethin-film coating is applied to the front surface of rear glass elementand incorporated into an electrochromic mirror, the overall reflectancedecreases and the transmittance increases.

According to a fourth example, a non-conductive three layer interferencecoating available from Libbey Owens Ford (LOF) of Toledo, Ohio, is usedin combination with a conductive fourth layer 188 of ITO or the like.The thin film stack available from LOF has a first layer 184 of Si, asecond layer 186 of SiO₂, and a third layer 187 of SnO₂. This coatinghas a reflectance of approximately 80 percent and a transmittance ofapproximately 4 percent for white light, and transmittance of 7 to 10percent for light having wavelengths in the 650 to 700 nm range. Thetransmittance in the 650 to 700 nm range makes this thin film stackparticularly suitable for a signal mirror that utilizes a red lightsource. While the SnO₂, SiO₂ and Si used in the LOF thin film stack arenot highly reflective materials by themselves (particularly when appliedas a thin layer), the alternating layers of such materials having highand low refractive indices produce the requisite high level ofreflectivity. The poor electrical conductivity of this thin film stackrequires that it be implemented with an electrically conductive layerthat has good electrical conductivity, such as a layer of ITO or thelike. The LOF thin film stack overcoated with an ITO layer having ahalf-wave thickness exhibited a sheet resistance of 12 Ω/Y. When theITO/LOF thin-film stack was used as a second electrode for anelectrochromic mirror, the mirror had a reflectance of 65 percent.Several different displays were placed behind the assembled mirror andwere all easily observed.

FIG. 7G shows yet another alternate construction that is very similar tothat shown in FIG. 7F, with the exception that only three layers areutilized for the electrically conductive multi-layer thin-film coating190. According to the construction shown in FIG. 7G, thin-film coating190 includes a first layer 184 made of a material having a highrefractive index such as the materials noted above in connection withFIG. 7F, a second layer made of a material having a low refractive indexsuch as those materials also discussed above for layer 186 in FIG. 7F,and a third layer 188 of electrically conductive material. Layer 188need not be made of a material having a high refractive index, butrather may be made of any electrically conductive material suitable foruse in an electrochromic mirror. For example, layer 188 may be a highlyreflective metal, such as silver or a silver alloy, or may be a metaloxide, such as ITO. To illustrate the feasibility of such a coating, twoexamples are described below.

In a first example, an electrochromic mirror was modeled having a firstlayer 184 of ITO deposited on a front surface of rear glass substrate114 at a thickness of 590 Å, a second layer 186 of silicon dioxideapplied at a thickness of 324 Å over first layer 184, and a third layer188 of silver having a thickness of 160 Å applied over second layer 186.The electrochromic mirror was then illuminated with a CIE illuminant D65white light source at an angle of incidence of 20°. When illuminatedwith such white light, the mirror exhibited a luminance reflectance of52 percent and a* and b* values of approximately 1.0 and 5.0,respectively. When illuminated with a red LED source at 35° angle ofincidence, the mirror exhibited a luminous transmittance of 40 percent.

According to a second example of the structure shown in FIG. 7G, anelectrochromic mirror was modeled having a first layer 184 of silicondeposited at a thickness of 184 Å on the front surface of glasssubstrate 114, a second layer 186 deposited on first layer 184 andformed of silicon dioxide at a thickness of 1147 Å, and a third layer188 of ITO of a thickness of 1076 Å applied over second layer 186. Theelectrochromic mirror having such a coating was illuminated with a CIEilluminant D65 white light source at 20° angle of incidence. Whenmodeled as illuminated with such white light, the modeled mirrorexhibited a luminous reflectance of 54 percent and a* and b* values of−2.5 and 3.0, respectively. When modeled as illuminated with a red LEDsource at 35° angle of incidence, the modeled mirror exhibited aluminous transmittance of approximately 40 percent.

Considering that the above two three-layer examples exhibited luminousreflectance in excess of 50 percent and transmittance of approximately40 percent, a mirror constructed as shown in FIG. 7G meets the specificobjectives noted above with respect to FIG. 7F, and is thereforesuitable for use in an outside electrochromic rearview mirrorincorporating a signal light.

As will be apparent to those skilled in the art, the electricallyconductive multi-layer thin-film coating described above may beimplemented as a third surface reflector for an electrochromic mirrorregardless of whether the electrochromic medium is a solution-phase,gel-phase, or hybrid (solid state/solution or solid state/gel).

FIG. 7H shows yet another alternative construction for the presentinvention. This embodiment is similar to that shown in the abovefigures, and is most similar to that shown in FIGS. 7A and 7B.Specifically, in the most preferred form, a layer of highly reflectivematerial 121 is provided along with a coating 172, which comprises afirst layer 174 and a second layer 176. First layer 174 is preferably atransparent conductive material and most preferably is formed of ITO.Second layer 176 of coating 172 is preferably reflective and mostpreferably made of chrome or a chrome alloy. Highly reflective layer 121is preferably made of silver alloy or any of the other highly reflectivematerials noted above. As shown in FIG. 7H, highly reflective layer 121is preferably masked within the region of window 146 to allow light froma display 170 to be transmitted through the mirror structure. Secondlayer 176 of coating 172 is also shown as being masked within the regionof window 146. It should be noted, however, that one or both layers 121and 176 need not be masked and may extend across the window 146, if itis desired to provide some reflectivity over and in front of display170.

Although the above alternative constructions shown and described withrespect to FIGS. 7A-7H do not include a flash-over protective layer orlayers such as layer 124 shown in FIG. 3, those skilled in the art willunderstand that such a flash-over layer may be applied over any of thevarious reflector/electrode 120 constructions shown in FIGS. 7A-7H.

FIG. 8 shows a cross section of one embodiment of the present inventionas similarly illustrated in FIG. 7E above. Specifically, by mounting alight emitting display assembly, indicator, enunciator, or othergraphics 170 behind a reflective layer such as layer 178, spuriousreflections occur at various interfaces within the electrochromic mirrorthat result in one or more ghost images being readily viewable by thevehicle occupants. The perceived separation between these imagesincreases as the reflective surfaces move further apart. In general, thethinner the glass used in the mirror construction, the lessobjectionable the images become. However, eliminating or reducing theintensity of the spurious reflections enhances the overall clarity ofthe display. As shown in FIG. 8, a point of illumination from display170 emits light through element 114 as illustrated by light rays A andB, which are only two of an infinite number of light rays that could betraced from any one point source. Light rays A and B are thentransmitted through transparent conductive layer 172 with little or noreflections at the interface between electrode 172 and element 114 dueto the closeness of the indices of refraction of these two components.The light then reaches the interface between transparent layer 172 andreflective layer 178, where between 10 and 20 percent of the light istransmitted through reflective layer 178 into electrochromic medium 125.A large percentage of the light intensity striking reflective layer 178is thus reflected back as illustrated by light rays C and D. Whilereflected light that is incident upon a paint layer 182 on rear surface114 b of element 114 (ray C) may be absorbed substantially in itsentirety, light that is reflected back at display 170 (ray D) is notabsorbed by the layer of absorbent paint 182. Because many lightemitting displays, such as a vacuum fluorescent display with a glass topplate, an LCD, or any other display assembly mounted such that there isan air gap between surface 114 b and the front surface of display 170,typically include at least one specular surface 171, light reflectedback at the specular surface(s) 171 of display 170 (ray D) is reflectedoff surface 171 back through element 114, reflective electrode 120,electrochromic medium 125, layers 128 and 130, and element 112. Thisspurious reflection off the specular surface 171 of display 170 thuscreates a ghost image that is viewable by the vehicle occupants.Additional spurious reflections occur at the outer surface 112 a ofelement 112 due to the differences in refractive indices of element 112and the air surrounding the electrochromic mirror. Thus, lightrepresented by ray F is reflected back into the mirror from surface 112a and is subsequently reflected off of reflective layer 178 back thoughmedium 125, layers 128 and 130, and element 112. It is thereforedesirable to implement various measures that eliminate or reduce theintensity of these spurious reflections and thereby eliminate theannoying ghost images that are visible to the vehicle occupants. FIGS.9A-9D, which are described below, illustrate various modifications thatmay be made to reduce these spurious reflections. It should be notedthat these spurious reflections are always lower in brightness than thenonreflected image. One approach to improving the clarity of the displaywithout eliminating spurious reflections is to control the displaybrightness such that the intensity of the secondary images is below thevisual perception threshold. This brightness level will vary withambient light levels. The ambient light levels can be accuratelydetermined by photosensors in the mirror. This feedback can be used toadjust the display brightness so the secondary images are not brightenough to be objectionable.

Another way to reduce ghost images while also increasing the contrastratio between the light originating from the display and light reflectedfrom the surface of the transflective reflector is to provide a controlcircuit that is coupled to the display and coupled to the ambient andglare sensors typically provided in an electrochromic mirror assembly.The control circuit can determine whether daytime or nighttimeconditions are present as a function of the ambient light level sensedby the ambient sensor. During daytime conditions, the control circuitresponds to light levels sensed by the glare sensor to control acontrast ratio of light originating from the display and lightreflecting from the transflective area of the reflector. To control thecontrast ratio, the control circuit may increase the brightness of thedisplay and/or decrease the intensity of the light reflected from thetransflective surface by slightly reducing the transmittance of theelectrochromic medium. Typically, in electrochromic mirrors, the controlcircuit for controlling the electrochromic mirror determines whetherdaytime or nighttime conditions are present and, when daytime conditionsare present, the control circuit does not apply a voltage to theelectrochromic element such that the element is in its highesttransmission state. This was done to protect the anodic and cathodicspecies within the electrochromic medium from damage due to ultravioletradiation from the sun. However, recent advances in UV protection nowallow electrochromic mirrors to be darkened during daytime conditions.Accordingly, the contrast ratio may be enhanced during daytimeconditions by slightly darkening the electrochromic medium and therebyreducing the reflectivity of the mirror as a whole.

Because the ambient light levels may vary considerably during daytimeconditions, as in the case of a bright sunny day versus an overcast day,the output of the rearward facing glare sensor may be utilized as ameasure of the light levels incident upon the transflective layer of themirror. Thus, the contrast ratio may be variably controlled as afunction of the light sensed by the glare sensor during daytimeconditions. By selectively etching one of the electrodes in the regionin front of the display, selective darkening of the mirror may beaccomplished to only darken that portion in front of the display.

In prior art electrochromic mirrors utilizing displays, during daytimeconditions, the brightness of the display is typically set to a maximumvalue without variation while, during nighttime conditions, thebrightness of the display may be set to a lower fixed brightness level,or it may be variably controlled as a function of the dimming of themirror element. In such prior art devices, when an LED display isutilized, the brightness of the LED(s) is varied using a pulse-widthmodulated signal having a duty cycle that varies anywhere from 0 to 100percent. Such a pulse-width modulated signal is typically outputdirectly from the microprocessor. Depending upon the resolution of themicroprocessor, the number of intermediate steps of the pulse-widthmodulated signal may vary. In any event, the range of brightness throughwhich the LED(s) may be controlled is typically established by the rangeof brightness levels through which the LED may vary during nighttimeconditions. Accordingly, the dynamic range of brightness is somewhatlimited. This is because the LEDs are directly in the driver's field ofview and they must be very dim at nighttime. During the day, for safetyreasons, the brightness of the LED should be much brighter.

To increase the dynamic range, a control circuit constructed inaccordance with the present invention utilizes two different currentranges for driving the LED display depending upon whether nighttime ordaytime conditions are present. An exemplary control circuit forperforming this function is shown in FIG. 26. As illustrated, thecircuit includes a control circuit 900, which may include amicroprocessor also functioning as an inside mirror control circuit 230(FIG. 12), which is coupled to an ambient light sensor 232, a glaresensor 234, and an electrochromic element 920 having a constructionsimilar to those disclosed above. Thus, control circuit 900 may performvarious control functions for controlling the reflectivity ofelectrochromic mirror element 920 in response to light levels sensed byambient sensor 232 and glare sensor 234.

As mentioned above, one of the purposes of the circuit shown in FIG. 26is to control the brightness of one or more LEDs 902 of an indicator,signal light, or display. In general, the brightness of light emittedfrom an LED is a function of the current flowing through the LED.Control circuit 900 controls the amount of current flowing through LED902 by generating a pulse-width modulated signal 904 that is providedthrough a resistor 906 (e.g., 10 kΩ) to the base of a current-sourcingtransistor 908. The source of transistor 908 is coupled to LED 902 andthe drain is coupled to ground via a resistor 910 (e.g., 3 kΩ). Thedrain of transistor 908 is selectively coupled to ground via anothercurrent path through a resistor 912 (e.g., 300 Ω) and a switchingtransistor 914. The resistance of second resistor 912 is preferablysignificantly less than the resistance of resistor 910 such that whenswitching transistor 914 is conducting, the amount of current flowingthrough sourcing transistor 908 and LED 902 is significantly increased.The conducting status of switching transistor 914 is controlled inaccordance with a day/night signal 916 issued from control circuit 900and supplied to the base of transistor 914 via a resistor 918 (e.g., 10kΩ).

In operation, control circuit 900 monitors the output signal fromambient light sensor 232, which represents the ambient lightingconditions generally forward and above the vehicle. When the brightnesssensed by ambient sensor 232 exceeds a threshold, microprocessor 900determines that daytime conditions are present. Otherwise, it determinesthat nighttime conditions are present. Control circuit 900 may utilize ahysteresis to avoid excessive switching between daytime and nighttimecondition modes of operation. During nighttime conditions, controlcircuit 900 sets the level of day/night signal 916 to a level indicatingthat nighttime conditions exist, which correspondingly sets switchingtransistor 914 in a non-conductive state. Control circuit 900 may thenset the brightness level for LED 902 by generating an appropriate PWMsignal 904 causing sourcing transistor 908 to conduct current at a levelestablished by the PWM signal 904. Control circuit 900 may maintain thebrightness of LED 902 in a fixed state or may vary the brightness byvarying the duty cycle of PWM signal 904 in response to light levelssensed by glare sensor 234 and, optionally, light levels sensed byambient sensor 232. Also during nighttime conditions, control circuit900 controls the reflectivity of electrochromic mirror element 920 as afunction of the light sensed by glare sensor 234 and ambient sensor 232.

When daytime conditions are sensed by control circuit 900, controlcircuit 900 switches the state of day/night signal 916 thereby causingswitching transistor 914 to conduct current. This immediately increasesthe current flowing through sourcing transistor 908 and LED(s) 902thereby increasing the brightness of light output by LED 902. Thebrightness level of LED 902 either may then remain fixed or be varied byadjusting the duty cycle of PWM signal 904 as a function of the lightsensed by glare sensor 234. Additionally, control circuit 900 may beconfigured to slightly reduce the reflectivity of EC mirror element 920so as to increase the contrast ratio of the display/electrochromicmirror. The amount of reduction in the reflectivity of the EC mirrorelement 920 may be varied as a function of the light levels sensed byglare sensor 234.

Accordingly, as apparent from the above description and the structureshown in FIG. 26, the brightness of LED 902 may be varied throughout afirst range appropriate for nighttime conditions by varying the PWMsignal 904 between duty cycles of 0 and 100 percent and, during daytimeconditions, the brightness of LED 902 may be varied throughout a secondrange of brightness levels greater than that of the first range by alsovarying the duty cycle of the PWM signal 904 from between 0 and 100percent. This also allows the brightness level of the LED display to bemore precisely controlled during daytime and nighttime conditionsthrough ranges appropriate for such conditions.

Although the above-described circuit is utilized for controlling one ormore LEDs of a display, a similar arrangement may be configured forcontrolling the brightness of various other forms of displays that maybe utilized within a rearview mirror assembly or other vehicleaccessory.

Insofar as control circuit 900 is utilized to detect daytime andnighttime conditions, control circuit 900 may be configured to becoupled to various other displays 925 ₁-925 _(n), that are providedthroughout the vehicle via a vehicle bus interface 930 and the vehiclebus 935. Presently, displays in the instrument panel may be manuallyswitched between daytime and nighttime appropriate brightness levels orautomatically switched upon activation of the vehicle headlamps. Byutilizing the determination by control circuit 900 as to whether daytimeor nighttime conditions are present, an appropriate control signal maybe transmitted to the various displays 925 ₁-925 _(n), so as toautomatically change the brightness levels of each of these displayssimultaneously with the change in the brightness of any displays on therearview mirror and/or in the overhead console. The control signaloutput by control circuit 900 may be a simple day/night signal to causethe displays to toggle between two levels of brightness, or it maygenerate a signal that represents one of various brightness levelsthroughout a continuum for gradually varying the brightness levels ofall the displays as a function of the ambient light within and aroundthe vehicle. The control circuit 900 may thus control the brightness ofthe display throughout two different ranges of brightness levelsdepending upon the determination of whether it is daytime or nighttime.The first brightness range, which is associated with daytime conditions,may be disjoint (i.e., not overlap) from the second brightness range,which is associated with nighttime conditions. In such a case, theranges together may nevertheless represent different portions of a widercontinuous range of brightness levels. Alternatively, the ranges mayoverlap, and one range may be a subset of the brightness levels of theother range.

Although a specific embodiment is described above for determiningwhether daytime or nighttime conditions are present based upon anambient light level sensed by an ambient light sensor disposed on themirror housing, a similar determination may be made by monitoringambient light levels sensed by other light sensors in the vehicle, suchas sky or sunload sensors. The control circuit 900 making thedetermination may also be used to transmit a signal to control the stateof the vehicle's headlamps. As an alternative configuration, rather thandetermining whether daytime or nighttime conditions are present based onambient light levels, the control circuit may be configured to receive asignal indicating the status of the headlamps and use this headlampstatus information to determine whether daytime or nighttime conditionsare present.

Also in the above embodiment, the control circuit 900 varies thebrightness of the display as a function of the light level sensed by theglare sensor provided in the mirror. Those skilled in the art willappreciate, however, that any other or additional light sensor may beutilized for this purpose. Preferably, such a light sensor would providea measure of the light level of light directed at the mirror from therear or sides of the vehicle.

In the embodiment shown in FIG. 9A, anti-reflective means/structures 192and 194 are provided for reducing or preventing reflections fromspecular surface 171 and front surface 112 a of element 112,respectively. Anti-reflective means 192 may include an anti-reflectivefilm applied to the rear surface 114 b of element 114 or to any and allspecularly reflecting surfaces of display assembly 170. Anti-reflectivemeans 192 may also include a light absorbing mask applied to rearsurface 114 b or specular surface 171 of display assembly 170. Such amasking layer 192 may be made to cover substantially the entirety ofspecular surface 171, with the exception of those regions lying directlyover a light emitting segment of display 170. The masking may be madewith any light absorbing material, such as black paint, black tape,black foam backing, or the like. It should be noted that vacuumflorescent displays are available with an internal black mask in allareas around the individual light emitting elements. If anti-reflectivemeans 192 is formed as an anti-reflective layer, substantially any knownanti-reflective film may be employed for this purpose. Theanti-reflective film need only be constructed to prevent reflections atthe particular wavelength of the light emitted from display 170.

By providing anti-reflective means 192 as described above, any lightthat is reflected back from reflective layer 178 toward specular surface171 of display 170 is either absorbed or transmitted into display 170,such that it cannot be reflected from surface 171 through the devicetowards the eyes of the vehicle occupants. It should be noted thatanti-reflective means 192 may also include any other structure capableof reducing or preventing the reflection of light from specular surface171. Further, anti-reflective means 192 may include a combination of ananti-reflective film and a masking layer and layer 192 may beincorporated on any specularly reflective surface that could reflectlight reflected off reflector 178, for example, either the back surfaceof glass element 114, the front surface of display 170, or any internalsurface in display 170. The anti-reflective structure 192 may be in theform of a film or coating, or may be a structure provided by a surfacetreatment, such as a matte or other abraded or roughened finish. If ananti-reflection coating is applied to the internal surface of the frontpiece of glass in display 170, it is desirable to have the top surfaceof the anti-reflection coating be electrically conductive. In the caseof vacuum fluorescent displays, the inner surface of the top piece ofglass is preferably coated with a thin layer of a transparent conductivematerial such as ITO. This conductive layer is provided to bleed off anyelectrical charge that may develop during display operation. A glasssurface reflects about 4 percent of incident visible light. A glasssurface coated with 100 Å of ITO reflects about 6 percent of visibleincident light. If a glass surface is coated with a thin film stackconsisting of a base layer of 420 Å of ITO followed by 870 Å of SiO₂ andthen 100 Å of ITO, the surface reflectance can be reduced to about 0.5percent at a wavelength of 550 nm. The surface sheet resistance of theabove ITO/SiO₂/ITO film stack is less than 500 Ω/□. Other examples ofconductive anti-reflective stacks with a reflectance of about 0.5percent near 550 nm are 122 Å TiO₂/985 Å SiO₂/100 Å ITO and 578 ÅTiO₂/745 Å ITO. An example of an anti-reflective stack with a broaderlow reflection range is 240 Å TiO₂/242 Å SiO₂/553 Å TiO₂/694 Å SiO₂/100Å ITO. These anti-reflective stacks may be applied to not only the innersurface of the display glass, but additionally or alternatively upon anyof the surfaces of the display or mirror behind the reflective layer(s)of the mirror. Although a vacuum fluorescent display is discussed above,an anti-reflective stack could be applied to surfaces of an OLED, LCD,etc.

To further reduce reflections that may occur at the interfaces betweenthe mirror and the display, a refractive index matching material may beapplied between the display and the rear surface of the mirror.

To reduce the spurious reflections from the air interface with surface112 a of element 112, an anti-reflective film 194 may be provided onsurface 112 a. Anti-reflective film 194 may be formed of anyconventional structure. A circular polarizer inserted between thetransflective coating and the display is also useful in reducingspurious reflections.

FIG. 9B shows an alternative solution to the problems relating to thereflection of light from display 170 off reflective layer 178 and thespecular surface of the display. Specifically, display 170 is preferablyselected from those displays that do not include any form of specularsurface. Examples of such displays are available from Hewlett Packardand are referenced as the HDSP Series. Such displays generally have afront surface that is substantially light absorbing, such that little ifany light would be reflected off the forward-facing surface of thedisplay.

Another example of a display construction that would not have aspecularly reflecting surface (such as between glass and air) would be aback lit liquid crystal display (LCD) that is laminated directly ontothe back mirror surface 114 b to eliminate the air gap or air interfacebetween the display and the mirror. Eliminating the air gap is aneffective means of minimizing the first surface reflection of alldisplay devices. If the type of LCD used was normally opaque or darksuch as with a twisted nematic LCD with parallel polarizers or a phasechange or guest host LCD with a black dye, the reflected light would beabsorbed by the display and not re-reflected back toward the viewer.Another approach would be to use a back lit transmissive twisted nematicLCD with crossed polarizers. The entire display area would then beilluminated and contrasted with black digits. Alternatively, a positiveor negative contrast electrochromic display could be used in place ofthe LCD, or an organic LED could be laminated or fixed to the backsurface 114 b.

An alternative solution is shown in FIG. 9C, whereby display 170 ismounted in back of rear surface 114 b of rear element 114, such thatspecular surface 171 is inclined at an angle to rear surface 114 b. Asapparent from the ray tracings in FIG. 9C, any light emitted fromdisplay 170 that reflects off of reflective layer 178 back towardspecular surface 171 of display 170 is reflected off of specular surface171 at an angle which could direct the light beam away from the viewertowards, for instance, the roof of the vehicle or, if the angle of thedisplay is great enough, the beam could be directed toward an absorbingsurface such as a black mask applied to the back of the mirror onsurface 114 b. It should be noted that, rather than angling the display,the reflected beam could be deflected by some other means such as bylaminating a transparent wedge shape on the front of the display, thegoal being to redirect the reflected light out of the viewing cone ofthe display or to an absorbing media or surface.

As shown in FIG. 9E, another useful technique to reduce spuriousreflections is to reflect the display image off of a mirror surface 197(preferably a first surface mirror) at about a 45° angle and thenthrough the transflective layer 120. The image reflected off thetransflective layer 120 can then be redirected away from the specularsurfaces on the display by slightly angling the relationship of thedisplay to the transflective layer.

FIG. 9D shows yet another approach for overcoming the problems notedabove. Specifically, the embodiment shown in FIG. 9D overcomes theproblem by actually mounting the display in front of reflective layer178. To enable the display to be mounted in front of the reflectedlayer, a substantially transparent display, such as an organic lightemitting diode (OLED) 196 is utilized. OLEDs are available fromUniversal Display Corporation. Such OLEDs can be constructed such thatthey are thin transparent displays that could be mounted inside thechamber in which the electrochromic medium is maintained. Because OLED196 can be transparent, it would not interfere with the image viewed bythe driver of the vehicle. Additionally, by providing OLED 196 insidethe chamber between the substrates, display 196 is protected from anyadverse environmental effects. Thus, such an arrangement is particularlydesirable when mounting a display device in an exterior automotiverearview mirror. OLED 196 could be mounted on layer 178, layer 128,between layers 128 and 130, between layer 130 and element 112, betweenlayers 172 and 178, between layer 172 and element 114, to rear surface114 b of element 114, or to surface 112 a of element 112. Preferably,OLED display 196 is mounted in front of reflective layer 178 in thechamber between elements 112 and 114.

FIG. 9F shows yet another implementation utilizing an OLED 196. In thisimplementation, OLED 196 replaces one of elements 112 and 114 of theelectrochromic mirror structure. When used as a front element, the rearsurface of OLED 196 may be covered with a transparent conductor to serveas first electrode 128 or both the first and second electrodes may becarried on the third surface (i.e., the front surface of rear element114). Although not shown in FIG. 9F, OLED 196 may replace rear element114, in which case either a transparent electrode or a transflectiveelectrode 120 would be provided on its forward-facing surface. It wouldalso be possible to provide a reflector on the rear surface of OLED 196with a transparent conductor provided on its front surface whenreplacing element 114.

As shown in FIG. 9G, an electroluminescent display 950, preferably alight emitting polymer (LEP) display, may similarly be applied acrossthe entire front surface of the rearview mirror. Such a display mayreadily be provided by depositing an electrode 956 on the front surfaceof front element 112 of the mirror and by providing a front displaytransparent substrate 952 having disposed thereon a second electrode 954in sealed spaced-apart relation from the front surface of element 112. Aperipheral seal 958 similar to seal 116 may be provided between element112 and substrate 952. The sealed space defined between these elementsmay be filled with an LEP 960. By etching the transparent conductivesurfaces of one or both of electrodes 954 and 956, a segmented displaycan be created.

In use, the light level of display 950 may be adjusted so the reflectedimage would dominate the total image. By flashing a large but weakly litimage, an easy-to-read display can be created while still allowing fulluse of the mirror. A full-size, non-blocking display would eliminate theblind spot created by conventional displays. Being large and lighted,this display would serve as a better warning and information displaysince it would be able to get the driver's immediate attention as it isalways in the field of view. Such a large, easily seen display would bean ideal output for a GPS, navigational, or driver alert system. As anavigational display, it could show turns using a large arrow, displaydistance, and flash when a turn is missed, etc. Preferably, the LEPs 960that are utilized are transparent such that when power is not applied,display 950 is clear. Such transparent LEPs are available, particularlywhen used in a single color display.

While the above structure is described above in connection with arearview mirror, it would be possible to construct an electrochromicelement similar to that above without the reflective layer for use in anelectrochromic architectural window. In this case, the windows could besituated to be sources of light. A light emitting layer could thus makethe window a light source even if dimmed or at night. A light emittinglayer could also be used as either an internal or external decoration.If a lighted window is desired, but without a compromise in privacy, thedimmed electrochromic layer could be positioned on the inside of thewindow to maintain privacy while the light emitting layer could beprovided on the outside portion of the window to yield the desiredeffect. The lighted windows could be turned on and off to create othereffects.

To take advantage of the fact that the reflective layer in anelectrochromic mirror may be partially transmissive over its entiresurface area, a light collector may be employed behind the reflectivelayer to collect the light impinging on the mirror over a much largerarea than previously possible and to amplify the light as it is directedonto a photosensor. As will be described in more detail below, the useof such a light collector more than compensates for the lack of theprovision of an opening in the reflective layer and actually canincrease the sensitivity of the glare sensor in an electrochromicmirror.

FIG. 10 is a front view of an inside rearview mirror constructed inaccordance with the present invention. FIG. 11 is a cross-sectional viewtaken along plane 11-11′ of FIG. 10. According to this construction, thelight collector may be constructed as a plano-convex lens 609 mountedbehind a partially transmissive reflecting surface 607 and a variableattenuating layer 608. As shown in FIG. 11, lens 609 projects light fromsource 601 onto focal point 604 and light from source 601 a onto focalpoint 604 a. A small area sensor, for example, the active light sensorof U.S. patent application Ser. No. 09/237,107, filed on Jan. 25, 1999,now abandoned, which is incorporated herein by reference, is provided tosense glare from the rear viewed through lens 609, partiallytransmissive layer 607, and optionally through variable attenuatinglayer 608. This construction takes advantage of the fact that the activesensing area of sensor 605 is small, for example, 100 microns on a side,and that a relatively large light collector, lens 609 in this example,can be substantially hidden behind the partially transmissive mirror andconfigured so that relatively high optical gain may be provided for thesensor while still providing a characterized and relatively large fieldof view over which glare is sensed. In the example shown in FIG. 11,light source 601 a is approximately 20 degrees off the central axis andis close to the edge of the amplified field of view. Note thatunamplified light, part of which may not pass through the lens, may beused to maintain some sensitivity to glare over a larger field of view.

When designing a construction such as those shown in FIGS. 10 and 11,there are several design considerations. Because the source of lightthat impinges upon the mirror and creates glare is the head lamps ofautomobiles to the rear of the vehicle, and such light sources are at agreat distance away from the mirror relative to the size of the lens,the rays from an automotive head lamp light source are substantiallyparallel. With a good lens, most of the rays impinging on the lens froma source are projected to a relatively small, intense spot at the focalpoint 604. For a sensing position other than at the focal point, as afirst approximation, the optical gain is the ratio of the area of thelens through which light enters to that of the cross section of thefocussed cone in the plane where the light is sensed. In FIG. 11, with aspherical or aspherical lens 609, this would be the square of the ratioat the diameter of lens 609 to the length of line 610. This isapproximately 10 as depicted. If sensor 605 was placed at the focalpoint 604 as it would be if it were a pixel in an imaging array, nearlyall of the light passing through the lens from light source 601 wouldstrike sensor 605, making the optical gain very high. However, lightfrom a light source 601 a would totally miss the sensor and the field ofview would be extremely small. In FIG. 11, sensor 605 is placed at ahighly de-focussed point, which is common to the cones of light fromlight sources having positions for which optical gain should bemaintained. Note that the plane can optionally be chosen beyond thefocal point or other methods of diffusion may be used alone or incombination to widen and characterize the field of view. For asubstantially greater off-axis angle, the sensor will be outside of theprojected cone of light and no optical gain will be provided. Note thatto provide relatively high optical gain over a substantial field ofview, the collecting area should be quite large compared to the sensor.The area of the aperture should exceed the area of the sensor first byapproximately the ratio of the optical gain, and this ratio should bemultiplied by another large factor to provide a field of view having asolid angle that is much larger than that which would be imaged onto thesensor were it to be placed in the focal plane of the lens.

While this particular mirror construction has been described above asincluding a spherical or an aspherical lens 609, a Fresnel lens mayreplace the plano-convex lens depicted. Additionally, since for largefields of views the light rays must be redirected through even largerangles, totally internally reflecting (TIR) lenses or reflectors may beused and provide additional advantages. If, for example, a partiallytransmissive reflecting layer 607 with 20 percent transmission is chosenand an optical gain of 10 is used, the optical gain more than recoversthe loss incurred in passing through partially transmissive reflector607. Furthermore, no unsightly or expensive-to-produce aperture windowneeds to be provided for the sensor and control benefits of viewingthrough the layer are also realized.

In configurations where the viewing angle needs to be large in onedirection but relatively small in another, a cylindrical lens may beused. For example, to sense lights from vehicles in adjacent lanes, theviewing angle must be relatively large in the horizontal direction andthe viewing field may be relatively narrow in the vertical direction. Inthis case, lens 609 may be replaced by a cylindrical lens with ahorizontal axis. A stripe of light rather than a circle is projected,and since light gathering takes place in one rather than two directions,the benefit of the squaring effect for the relative areas of the lensaperture in the area of the projected light pattern in the plane of thesensor is lost. Optical gains of 5, for example, are still feasible,however. Composite lenses containing a patchwork of different elementsincluding, for example, sections of aspheric lenses with differentcenter positions and/or focal lengths, or even combinations of differentkinds of elements such as aspheric and cylindrical lenses may be used toretain reasonable optical gain and characterize the field of view. A rowof lens sections with stepped focal center points can serve well towiden the field of view in selected directions while maintaining a goodoverall optical gain. Some amount of diffusion is preferable in all thedesigns to prevent severe irregularity in the sensed light level due tosevere localized irregularities in the projected light pattern that areoften present. The extremely small area sensor will not average theseirregularities to any useful degree. Some lens designs may optionally becemented to the back of the mirror element.

In each of the constructions described above with respect to FIGS. 10and 11, any of the mirror constructions described above with respect toFIGS. 7A-7G may be employed for use as the electrochromic mirror(depicted as layers 607 and 608 in FIG. 11).

FIG. 12 shows an outside rearview mirror assembly 200 constructed inaccordance with another embodiment of the present invention. Outsiderearview mirror assembly 200 includes a mirror 210, which is preferablyan electrochromic mirror, an external mirror housing 212 having amounting portion 214 for mounting mirror assembly 200 to the exterior ofa vehicle, and a signal light 220 mounted behind mirror 210. To enablethe light from signal light 220 to project through electrochromic mirror210, a plurality of signal light areas 222 are formed in theelectrode/reflector of mirror 210 that include window regions containingelectrically conductive material that is at least partially transmissivesimilar to the information display and glare sensor window areasdescribed above with respect to the other embodiments of the presentinvention. Electrochromic mirror 210 may further include a sensor area224 disposed within the reflective coating on electrochromic mirror 210and similarly include window regions containing electrically conductivematerial that is at least partially transmissive so as to allow some ofthe incident light to reach a sensor mounted behind sensor area 224.Alternatively, sensor 224 could be used to sense glare in night drivingconditions and control the dimming of the exterior mirror independentlyor verify that the mirrors are being sufficiently dimmed by the controlcircuit in the interior mirror. In such a case, a more sensitive photosensor may be required, such as a CdS sensor.

Signal light 220 is preferably provided to serve as a turn signal lightand is thus selectively actuated in response to a control signalgenerated by a turn signal actuator 226. The control signal is thereforeapplied to signal light 220 as an intermittent voltage so as to energizesignal light 220 when a driver has actuated the turn signal lever. Asshown in FIG. 15, when vehicle B is in the blind spot of vehicle A wherethe driver of vehicle A cannot see vehicle B, the driver of vehicle Bcannot see the turn signal on the rear of vehicle A. Thus, if the driverof vehicle A activates the turn signal and attempts to change laneswhile vehicle B is in a blind spot, the driver of vehicle B may notreceive any advance notice of the impending lane change, and hence, maynot be able to avoid an accident. By providing a turn signal light in anoutside rearview mirror assembly 200 of vehicle A, the driver of anapproaching vehicle B will be able to see that the driver of vehicle Ais about to change lanes and may thus take appropriate action morequickly so as to avoid an accident. As illustrated in FIG. 15 anddescribed in more detail below, the signal light is preferably mountedwithin mirror assembly at an angle to the mirror surface to project thelight from the signal light outward into the adjacent lanes in the blindspot areas proximate the vehicle.

Referring again to FIG. 12, electrochromic mirror 220 may be controlledin a conventional manner by a mirror control circuit 230 provided in theinside rearview mirror assembly. Inside mirror control circuit 230receives signals from an ambient light sensor 232, which is typicallymounted in a forward facing position on the interior rearview mirrorhousing. Control circuit 230 also receives a signal from a glare sensor234 mounted in a rearward facing position of the interior rearviewmirror assembly. Inside mirror control circuit 230 applies a controlvoltage on a pair of lines 236 in a conventional manner, such that avariable voltage is applied essentially across the entire surface ofelectrochromic mirror 210. Thus, by varying the voltage applied to lines236, control circuit 230 may vary the transmittance of theelectrochromic medium in mirror 210 in response to the light levelssensed by ambient sensor 232 and glare sensor 234. As will be explainedfurther below, an optional third control line 238 may be connectedbetween the inside mirror control circuit 230 and a variable attenuator260 provided in outside mirror assembly 200, so as to selectivelyattenuate the energizing signal applied on lines 228 from turn signalactuator 226 to the signal light 220 in response to the control signalsent on line 238. In this manner, inside mirror control circuit 230 mayselectively and remotely control the intensity of signal light 220 basedupon information obtained from sensors 232 and 234 and thereby eliminatethe need for a sensor to be mounted in each mirror assembly as well asthe associated sensor area 224.

Mirror assembly 200 may further include an electric heater (not shown)provided behind mirror 210 that is selectively actuated by a heatercontrol circuit 240 via lines 242. Such heaters are known in the art tobe effective for deicing and defogging such external rearview mirrors.Mirror assembly 200 may optionally include a mirror position servomotor(not shown) that is driven by a mirror position controller 244 via lines246. Such mirror position servomotors and controls are also known in theart. As will be appreciated by those skilled in the art, mirror assembly200 may include additional features and elements as are now known in theart or may become known in the future without departing from the spiritand scope of the present invention.

An exemplary signal light subassembly 220 is shown in FIG. 13. Such asignal light 220 is disclosed in U.S. Pat. Nos. 5,361,190 and 5,788,357,which disclose the signal light in combination with dichroic exteriorrearview mirrors that are not electrochromic. The disclosures of thesignal light assembly in U.S. Pat. Nos. 5,361,190 and 5,788,357 areincorporated herein by reference. As explained below, however, the samesignal light subassembly may be used in connection with anelectrochromic mirror as may modified versions of the signal lightsubassembly shown in FIG. 13.

As shown in FIG. 13, signal light 220 includes a printed circuit board250 that, in turn, is mounted within a housing 252 having a peripheraledge that serves as a shroud (see FIGS. 6A and 6B) to block any straylight from exiting the signal light assembly. Signal light 220preferably includes a plurality of LEDs 254 that are mounted to circuitboard 250. LEDs 254 may be mounted in any pattern, but are preferablymounted in a pattern likely to suggest to other vehicle operators thatthe vehicle having such signal mirrors is about to turn. LEDs 254 may beLEDs that emit red or amber light or any other color light as may provedesirable. LEDs 254 are also preferably mounted to circuit board 250 atan angle away from the direction of the driver. By angling LEDs relativeto mirror 210, the light projected from LEDs 254 may be projectedoutward away from the driver towards the area C in which the driver ofanother vehicle would be more likely to notice the signal light, asshown in FIG. 15. Hence, the potential glare from the signal light asviewed by the driver may be effectively reduced.

Signal light 220 may optionally include a day/night sensor 256 alsomounted to circuit board 250. If sensor 256 is mounted on circuit board250, a shroud 257 is also preferably mounted to shield sensor 256 fromthe light generated by LEDs 254. Also, if sensor 256 is provided insignal light 220, a day/night sensing circuit 258 may also be mounted oncircuit board 250 so as to vary the intensity of LEDs 254 in response tothe detection of the presence or absence of daylight by sensor 256.Thus, if sensor 256 detects daylight, circuit 258 increases theintensity of the light emitted from LEDs 254 to their highest level anddecreases the intensity of the emitted light when sensor 256 detectsthat it is nighttime. The above-noted signal light disclosed in U.S.Pat. Nos. 5,361,190 and 5,788,357 includes such a day/night sensor 256and associated control circuit 258, and therefore, further descriptionof the operation of the signal light in this regard will not beprovided.

As an alternative to providing a day/night sensor 256 in each of thevehicle's exterior rearview mirrors, a variable attenuator 260 or othersimilar circuit may be provided to vary the driving voltage applied fromthe turn signal actuator 226 on line 228 in response to a control signaldelivered from inside mirror control circuit 230 on a dedicated line238. In this manner, inside mirror control circuit 230 may utilize theinformation provided from ambient light sensor 232 as well as theinformation from glare sensor 234 to control the intensity of the lightemitted from LEDs 254 and signal light 220. Since the ambient light andglare sensors 232 and 234 are already provided in an internalelectrochromic rearview mirror, providing for such remote control by theinside mirror control circuit 230 eliminates the need for providingadditional expensive sensors 256 in the signal light 220 of eachexterior mirror assembly. As an alternative to running a separate wire258 to each of the outside rearview mirrors, variable attenuator 260 maybe provided in the dashboard proximate the turn signal actuator orotherwise built into the turn signal actuator, such that a singlecontrol line 238′ may be wired from inside mirror control circuit 230 tothe turn signal actuator as shown in FIG. 12.

The intensity of the light emitted from the LEDs may thus be varied as afunction of the light level sensed by ambient sensor 232 or glare sensor234, or as a function of the light levels sensed by both sensors 232 and234. Preferably, LEDs 254 are controlled to be at their greatestintensity when ambient sensor 232 detects daylight and at a lesserintensity when sensor 232 detects no daylight. Because the transmittanceof the electrochromic medium is decreased when excessive glare isdetected using glare detector 234, the intensity of LEDs 254 ispreferably correspondingly increased so as to maintain a relativelyconstant intensity at nighttime.

Electrochromic mirror 210 may be constructed in accordance with any ofthe alternative arrangements disclosed in FIGS. 7A-7H above, where lightsource 170 represents one of LEDs 254 of signal light subassembly 220.Accordingly, each possible combination of the various constructionsshown in FIGS. 7A-7H with signal light subassembly 220 are notillustrated or described in further detail. As but one example, however,FIG. 14 shows the manner in which a signal light subassembly 220 couldbe mounted behind a preferred construction that is otherwise identicalto that shown in FIG. 7C. As apparent from a comparison of FIG. 7C andFIG. 14, each of signal light areas 222 corresponds to window 146 ofFIG. 7C. As discussed above, for an outside rearview mirror thereflectance of reflector/electrode 120 is preferably at least 35 percentand the transmittance is preferably at least 20 percent so as to meetthe minimum reflectance requirements and yet allow sufficienttransmittance so that the light emitted from signal light 220 may bereadily noticed by the driver of an approaching vehicle.

FIG. 16 shows a front elevational view schematically illustrating aninside mirror assembly 310 according to an alternative embodiment of thepresent invention. Inside mirror assembly 310 may incorporatelight-sensing electronic circuitry of the type illustrated and describedin the above-referenced Canadian Patent No. 1,300,945, U.S. Pat. No.5,204,778, or U.S. Pat. No. 5,451,822, and other circuits capable ofsensing glare and ambient light and supplying a drive voltage to theelectrochromic element.

Rearview mirrors embodying the present invention preferably include abezel 344, which conceals and protects the spring clips (not shown) andthe peripheral edge portions of the sealing member and both the frontand rear glass elements (described in detail below). Wide varieties ofbezel designs are well known in the art, such as, for example, the bezeldisclosed in above-referenced U.S. Pat. No. 5,448,397. There is also awide variety of known housings for attaching the mirror assembly 310 tothe inside front windshield of an automobile; a preferred housing isdisclosed in above-referenced U.S. Pat. No. 5,337,948.

The electrical circuit preferably incorporates an ambient light sensor(not shown) and a glare light sensor 360, the glare light sensor beingcapable of sensing glare light and being typically positioned behind theglass elements and looking through a section of the mirror with thereflective material partially removed in accordance with this particularembodiment of the present invention. Alternatively, the glare lightsensor can be positioned outside the reflective surfaces, e.g., in thebezel 344. Additionally, an area or areas of the third surfacereflective electrode, such as 346, may be partially removed inaccordance with the present invention to permit a display, such as acompass, clock, or other indicia, to show through to the driver of thevehicle. The present invention is also applicable to a mirror which usesonly one video chip light sensor to measure both glare and ambient lightand which is further capable of determining the direction of glare. Anautomatic mirror on the inside of a vehicle, constructed according tothis invention, can also control one or both outside mirrors as slavesin an automatic mirror system.

FIG. 17 shows a cross-sectional view of mirror assembly 310 along theline 17-17′. Like the above-described embodiments, mirror 310 has afront transparent element 112 having a front surface 112 a and a rearsurface 112 b, and a rear element 114 having a front surface 114 a and arear surface 114 b. Since some of the layers of the mirror are verythin, the scale has been distorted for pictorial clarity. A layer of atransparent electrically conductive material 128 is deposited on thesecond surface 112 b to act as an electrode. Transparent conductivematerial 128 may be any of the materials identified above for the otherembodiments. If desired, an optional layer or layers of a colorsuppression material 130 may be deposited between transparent conductivematerial 128 and front glass rear surface 112 b to suppress thereflection of any unwanted portion of the electromagnetic spectrum.

At least one layer of a material that acts as both a reflector and aconductive electrode 120 is disposed on third surface 114 a of mirror310. Any of the materials/multi-layer films described above maysimilarly be used for reflector/electrode 120. U.S. Pat. No. 5,818,625entitled “DIMMABLE REARVIEW MIRROR INCORPORATING A THIRD SURFACE METALREFLECTOR” and filed on or about Apr. 2, 1997, describes anotherreflector/electrode 120 in detail. The entire disclosure of this patentis incorporated herein by reference.

In accordance with this embodiment of the present invention, a portionof conductive reflector/electrode 120 is removed to leave an informationdisplay area 321 comprised of a non-conducting area 321 a (to view adisplay) and a conducting area 321 b (to color and clear theelectrochromic medium), as shown in FIG. 17. Although only shown indetail for the display area 321, the same design may be, and preferablyis, used for the glare sensor area (160 in FIG. 16). FIG. 18 shows afront elevational view illustrating information display area 321. Again,since some of the layers of this area are very thin, the scales of thefigures have been distorted for pictorial clarity. The portion ofconductive reflector/electrode that is removed 321 a is substantiallydevoid of conductive material, and the portion not removed should be inelectrical contact with the remaining area of reflector/electrode 120.That is to say, there are little or no isolated areas or islands ofreflector/electrode 120 that are not electrically connected to theremaining portions of the reflector/electrode 120. Also, although theetched areas 321 a are shown as U-shaped (FIG. 17), they may have anyshape that allows sufficient current flow through lines 321 b whileallowing the driver to view and read the display 170 through etchedareas 321 a. The reflector/electrode 120 may be removed by varyingtechniques, such as, for example, by etching (laser, chemical, orotherwise), masking during deposition, mechanical scraping,sandblasting, or otherwise. Laser etching is the presently preferredmethod because of its accuracy, speed, and control.

The information display area 321 is aligned with a display device 170such as a vacuum fluorescent display, cathode ray tube, liquid crystal,OLED, flat panel display and the like, with vacuum fluorescent displaybeing presently preferred. The display 170, having associated controlelectronics, may exhibit any information helpful to a vehicle occupant,such as a compass, clock, or other indicia, such that the display willshow through the removed portion 321 a to the vehicle occupant.

The area that is substantially devoid of conductive reflector/electrode321 a and the area having conductive reflector/electrode present 321 bmay be in any shape or form so long as there is sufficient area havingconductive material to allow proper coloring and clearing (i.e.,reversibly vary the transmittance) of the electrochromic medium, whileat the same time having sufficient area substantially devoid ofconductive material to allow proper viewing of the display device 170.As a general rule, information display area 321 should haveapproximately 70-80 percent of its area substantially devoid ofconductive material 321 a and the conductive material 321 b filling theremaining 20-30 percent. The areas (321 a and 321 b) may have a varietyof patterns such as, for example, linear, circular, elliptical, etc.Also, the demarcation between the reflective regions and the regionsdevoid of reflective material may be less pronounced by varying thethickness of the reflective materials or by selecting a pattern that hasa varying density of reflective material. It is presently preferred thatareas 321 a and 321 b form alternating and contiguous lines (see FIG.17). By way of example, and not to be construed in any way as limitingthe scope of the present invention, the lines 321 b generally may beapproximately 0.002 inch wide and spaced approximately 0.006 inch apartfrom one another by the lines substantially devoid of conductivematerial. It should be understood that although the figures show thelines to be vertical (as viewed by the driver), they may be horizontalor at some angle from vertical. Further, lines 321 a need not bestraight, although straight vertical lines are presently preferred.

If all of the third surface reflector/electrode 120 is removed in theinformation display area 321 or in the area aligned with the glare lightsensor 160, there will be significant coloration variations betweenthose areas and the remaining portion of the mirror where thereflector/electrode 120 is not removed. This is because for everyelectrochromic material oxidized at one electrode there is acorresponding electrochromic material reduced at the other electrode.The oxidation or reduction (depending on the polarity of the electrodes)that occurs on the second surface directly across from the informationdisplay area 321 will occur uniformly across the area of the informationdisplay area. The corresponding electrochemistry on the third surfacewill not, however, be uniform. The generation of light-absorbing specieswill be concentrated at the edges of the information display area (whichis devoid of reflector/electrode). Thus, in the information display area321, the generation of the light-absorbing species at the second surfacewill be uniformly distributed, whereas the light-absorbing species atthe third surface will not, thereby creating aesthetically unappealingcolor discrepancies to the vehicle occupants. By providing lines ofreflector/electrode 120 areas throughout the information display area321, in accordance with the present invention, the generation oflight-absorbing species (at the second and third surfaces) in theinformation display area will be much closer to the uniformity seen inother areas of the mirror with completely balanced electrodes.

Although those skilled in the art will understand that manymodifications may be made, the laser etching may be accomplished byusing a 50 watt Nd:YAG laser, such as that made by XCEL Control Laser,located in Orlando, Fla. In addition, those skilled in the art willrealize that the power settings, the laser aperture, the mode of thelaser (continuous wave or pulsed wave), the speed with which the lasermoves across the surface, and the wave form of the laser may be adjustedto suit a particular need. In commercially available lasers, there arevarious wave forms that the laser follows while it ablates the surfacecoatings. These wave forms include straight lines, sine waves at variousfrequencies and ramp waves at various frequencies, although many othersmay be used. In the presently preferred embodiments of the presentinvention, the areas devoid of reflective material 321 a are removed byusing the laser in a pulsed wave mode with a frequency of about 3 kHz,having a narrow (e.g., around 0.005 inch) beam width where the laser ismoved in a straight line wave form.

FIGS. 14B and 14C show two alternate arrangements for implementing thepresent invention. FIGS. 14B and 14C are partial cross-sectional viewstaken along lines 14-14′ of FIG. 12. FIG. 14B shows an arrangementsimilar to that of the inside rearview mirror shown in FIG. 17 in whichparallel lines of reflector/electrode material 222 b are provided acrossthe signal light area 222 by either etching out or masking lines 222 ain regions that are devoid of the reflector/electrode material. Each ofthe signal light areas 222 is provided in a position on the rearviewmirror corresponding and overlying one of LEDs 254 as apparent from acomparison of FIGS. 12 and 13. Electrochromic mirror 410 may beconstructed in the same manner as described above for the insiderearview mirror 310 of the preceding embodiment. Specifically, mirror410 includes a front transparent element 112 having a front surface anda rear surface, and a rear element 114 having a front surface 114 a anda rear surface 114 b. Mirror 410 also includes a layer 128 of atransparent conductive material deposited on the rear surface of frontelement 112 or on an optional color suppression material 130 that isdeposited on the rear surface of front element 112. Additionally, mirror410 includes at least one layer 120 disposed on a front surface 114 a ofrear element 314 that acts as both a reflector and a conductiveelectrode. An electrochromic medium is disposed in a chamber definedbetween layers 128 and 120. All of the component elements of mirror 410may be made using the same materials and applied using the sametechniques as described above with respect to the preceding embodiments.Preferably, however, the reflector/electrode material of layer 120 ismade using nickel, chrome, rhodium, ruthenium, stainless steel, silver,silver alloys, platinum, palladium, gold, or combinations/alloysthereof.

The reflectance of the mirror in the signal light areas 222 or sensorarea 224 may also be controlled by varying the percentage of those areasthat are devoid of reflective material or by varying the thickness ofthe reflector/electrode coating. Further, the reflector/electrodematerial used to form lines 222 b in signal light area may be differentfrom the reflector/electrode material used for the remainder of themirror. For example, a reflector/electrode material having a higherreflectance may be used in the signal light area such that thereflectivity in the signal light area is the same as that of theremainder of the mirror despite the regions therein that are devoid ofreflector material. Preferably, the region of the signal light area thatis devoid of reflective material constitutes between 30 and 50 percentof the signal light area and the area occupied by the reflectivematerial is between 50 and 70 percent of the signal light area. Toachieve these percentages, the lines of reflector/electrode material arepreferably about 0.010 inch wide and the spaces between the lines areabout 0.006 inch wide.

The arrangement shown in FIG. 14C differs from that shown in FIG. 14B inthat the reflective material is formed on the fourth surface (i.e., therear surface 114 b of rear element 114). With such an arrangement, theelectrode 340 on the third surface is preferably made of a transparentmaterial similar to that of the electrode 128 formed on the rear surfaceof front element 112. Like the arrangement shown in FIG. 14B, thestructure shown in FIG. 14C includes a signal light area 222 havingalternating regions of reflective material 222 b and regions devoid ofsuch reflective material 222 a. In this manner, LEDs 254 may be morecovertly hidden from view by the driver and yet light from LEDs 254 mayproject through all the layers of electrochromic mirror 410 so as to bevisible by drivers of other vehicles. Similarly, if a day/night sensor256 is provided, a sensor area 224 may be provided in the same mannerwith alternating regions of reflective material 224 b and regions thatare void of reflective material 224 a.

A benefit of utilizing the above-described structure in connection witha signal light is that the use of a dichroic coating may be avoided.Dichroic coatings are generally nonconductive and therefore cannot beused in an electrochromic mirror having a third surface reflector. Also,the only current dichroic coatings that are economically feasible arethose that transmit red and infrared light and reflect other colors oflight. Thus, to construct a practical signal light, only LEDs that emitred light may be utilized. Accordingly, there is little flexibility inthis regard when a dichroic coating is utilized. To the contrary, withthe structure of the present invention, any color signal light may beused.

The concept of providing a window region having alternating areas devoidof reflective material may similarly be applied to a non-electrochromicsignal mirror. And although other materials may be used, chromium on thefirst or second surface of such a non-electrochromic mirror is thepresently preferred reflective material.

FIGS. 14D and 19 show yet another embodiment of the present invention asit pertains to signal mirrors. According to this embodiment, the signalmirror includes an additional structure for rendering the signal lightmore covert with respect to the field of view of the driver. While eachof the embodiments relating to the signal mirrors discussed abovecovertly hides the signal light behind the mirror when they are notenergized and generally hides the signal light when activated, thereremains the possibility with such embodiments that the driver may bedistracted during the periods in which the signal light is activated.Specifically, while the LEDs of the signal light are angled outward awayfrom the driver's eyes, the driver may still be able to see the LEDs aspoints of light through portions of the mirror assembly. Accordingly,this embodiment provides means for reducing the transmission of lightfrom the signal light through the mirror in the direction of the driver.As explained below, this additional means may take on severalalternative or additive forms.

Referring to FIG. 14D, a construction is shown whereby a baffle assembly500 is positioned between signal light assembly 220 and the rear surfaceof mirror assembly 510. The particular baffle assembly 500 shown in FIG.14D includes a forward, upper plate 502 and a rearward, lower plate 504fixed in spaced and parallel relation by a plurality of legs 506. Asillustrated in FIGS. 14D and 19, lower plate 504 is laterally displacedrelative to forward plate 502 in a more outward position away from thedriver. Lower plate 504 includes a plurality of apertures 508corresponding in size and position to each of LEDs 254. Upper plate 502is disposed relative to aperture 508 and slightly over LEDs 254 so as toblock the driver's view of LEDs 254. Upper plate 502 includes anaperture 509 through which light may pass so as to reach sensor 256. Thespaces between upper plate 502 and lower plate 504 as well as apertures508 in lower plate 504 provide a sufficient opening for light projectedfrom the angled LEDs 254 to be transmitted through mirror 510 and intoregion C shown in FIG. 15. Baffle assembly 500, as shown, is preferablymade of a black plastic or the like.

The functionality of baffle assembly 500 may be supplemented oralternatively performed by various other mechanisms designated generallyin FIG. 14D by reference numeral 520. Specifically, element 520 may beany one or a combination of a light control film, a layer of black ordark paint, or a heater element. A light control film, such as thatavailable from the 3M Company under the trade designation LCF-P, may beused, which is a thin plastic film enclosing a plurality of closelyspaced, black colored microlouvers. Such a light control film isdisclosed for use in a conventional signal mirror in U.S. Pat. Nos.5,361,190 and 5,788,357, the disclosures of which are herebyincorporated by reference. As disclosed in those patents, such a lightcontrol film may have a thickness of 0.030 inches, with the microlouversspaced approximately 0.005 inches apart. The microlouvers are typicallyblack and are positioned at various angular positions to provide asuitable viewing angle. Such a light control film permits light fromLEDs 254 to be transmitted at the appropriate viewing angle to reachregion C (FIG. 15). The light control film also serves to block thelight projected from LEDs 254 from travelling outside the appropriateviewing angle in the line of sight of the driver. Thus, unlike thebaffle assembly 500 depicted in FIGS. 14D and 19, such a light controlfilm may be placed completely over and in front of each of LEDs 254.Further, such a light control film could also be made using other formsof optical elements, such as holograms and the like.

If element 520 is a coating of an opaque paint, such a coating would notextend far enough in front of the LEDs to block light from LEDs 254 tobe transmitted through mirror 510 into blind spot area C (FIG. 15).Alternatively, such a coating of paint could extend completely in frontof LEDs 254, provided it was configured to have some form of louver orequivalent structure formed in its surface in the areas of the intendedtransmission path of LEDs 254. For example, the thickness of such apaint coating could be controlled to create effective louvers usingscreen-printing, molding, stamping, or laser ablation. Further, ifreflector/electrode 120 is configured in the manner described above withrespect to FIGS. 14B and 14C, element 520 could be a coating of blackpaint that has similar bars or stripes in the areas overlying LEDs 254while having spacial relations relative to the bars 222 b ofreflector/electrode 120, so as to provide a transmission path at theappropriate angle for vehicles to view the lights when in the vehicle'sblindspots, while blocking the light from the field of view of thedriver. Further, as shown in FIG. 14D, the bars 222 b ofreflector/electrode 120 may be configured to have varying widths thatdecrease with increasing distance from the driver, so as to reduceperipheral transmittance through area 222 in the direction of thedriver, or may have a less pronounced edge definition, as discussedabove.

If element 520 is provided using a mirror heating element, the heatingelement could be provided to extend across the entire fourth surface ofthe mirror and have apertures formed in appropriate locations to allowlight emitted from LEDs 254 to be transmitted at the appropriate angle.

Another mechanism for shielding the driver from light emitted from LEDs254 is to increase the thickness of the reflector/electrode 120 in aregion 530 corresponding to that of upper plate 502 thereby reducing thetransmittance through that portion of reflector/electrode 120.Currently, such reflector/electrodes have a transmittance ofapproximately 1-2 percent. To sufficiently shield the driver from lighttransmitted from LEDs 254, reflector/electrode 120 preferably has athickness in region 530 that reduces the transmittance therethrough toless than 0.5 percent, and more preferably to less than 0.1 percent.

Element 520 may additionally or alternately include various opticalfilms, such as a prismatic or Fresnel film or a collimating opticalelement as described in U.S. Pat. No. 5,788,357 so as to collimate anddirect the light emitted from LEDs 254 at the appropriate angle withoutalso transmitting light in the direction of the driver.

As yet another possible solution, sidewalls 252 of light assembly 220may be extended so as to space LEDs 254 further from the rear surface ofmirror assembly 510, such that sidewalls 252 effectively block any lightfrom LEDs 254 from being transmitted in the direction of the driver ofthe vehicle.

Although the structure shown in FIG. 14D shows mirror assembly 510 asincluding the reflector/electrode 120 as illustrated in the embodimentshown in FIG. 14B above, mirror assembly 510 could take on any of theother forms discussed above with respect to the embodiment describedwith respect to FIG. 14A or FIGS. 7A-7H.

Although the present invention has been described as providing a signallight that is used as a turn signal, it will be appreciated by thoseskilled in the art that the signal light could function as any otherform of indicator or signal light. For example, the signal light couldindicate that a door is ajar so as to warn drivers of approachingvehicles that a vehicle occupant may be about to open a door intooncoming traffic, or the light behind the mirror may be an indicatorlight to indicate that the mirror heaters have been turned on, thatanother vehicle is in a blind spot, that the pressure is low, that aturn signal is on, or that freezing/hazardous conditions exist.

While the signal light of the present invention has been described aboveas preferably being made of a plurality of LEDs, the signal light maynevertheless be made of one or more incandescent lamps, or any otherlight source, and an appropriately colored filter without departing fromthe spirit or scope of the present invention.

Yet another embodiment of the present invention is shown in FIGS. 20-22.In this embodiment, an exterior rearview mirror assembly 700 is providedhaving a housing 710 adapted for attachment to the exterior of avehicle. Such mirrors are often mounted to the vehicle door 730 or tothe A-pillar of the vehicle. Within housing 710 are a mirror structure720 and a light source 725 mounted behind mirror structure 720. Mirror720 may be constructed in accordance with any of the above-notedembodiments, such that light emitted from light source 725 may beprojected through mirror 720. Mirror 720 may thus have a reflectorhaving a masked window portion in front of light source 725 or may havea region 726 that is at least partially transmissive provided in frontof light source 725. As yet another alternative, the region 726 in frontof light source 725 may have a construction similar to that shown inFIG. 14 or the entire reflector in mirror 720 may be partiallytransmissive. As shown in FIGS. 21 and 22, light source 725 ispreferably mounted such that it projects light onto a region of thevehicle door 730 on which the vehicle door handle 735 and lock mechanism737 are provided. Lock mechanism 737 may be a keyhole or touch pad ascommonly used to enable the vehicle doors to be locked or unlocked.

Light source 725 may be any type of light source, and is preferably awhite light source. A preferred light source is disclosed incommonly-assigned U.S. patent application Ser. No. 09/426,795, entitled“SEMICONDUCTOR RADIATION EMITTER PACKAGE,” filed on Mar. 15, 1999, byJohn K. Roberts, now U.S. Pat. No. 6,335,548; U.S. patent applicationSer. No. 09/425,792, entitled “INDICATORS AND ILLUMINATORS USING ASEMICONDUCTOR RADIATION EMITTER PACKAGE,” filed on Oct. 23, 1999, byJohn K. Roberts et al., now U.S. Pat. No. 6,441,943; and U.S. patentapplication Ser. No. 09/835,278, entitled “RADIATION EMITTER DEVICES ANDMETHOD OF MAKING THE SAME,” filed on Apr. 13, 2001, by John K. Robertset al., now U.S. Pat. No. 6,521,916, the entire disclosures of which areincorporated herein by reference.

Light source 725 may be activated so as to project light in response tothe same actions to which the interior vehicle lights are turned on andoff when providing illuminated entry into the vehicle. Thus, forexample, light source 725 may illuminate a portion of door 730 when aperson depresses the lock or unlock key on a key fob associated with thevehicle for remote keyless entry (RKE), when a person attempts to openthe door, or when a person inserts a key into the lock mechanism 737.Alternatively, a motion sensor may be provided to activate light source725. Preferably, light source 725 is disabled so as to be incapable ofprojecting light when the vehicle's ignition has been turned on.

By providing such a light source 725 within exterior rearview mirrorhousing 710, a light source may be mounted on the vehicle forilluminating the area on the exterior of the vehicle where a vehicleoccupant must contact to enter the vehicle. Such a feature isadvantageous when the vehicle is parked in particularly dark locations.

While light source 725 has been described as being mounted to projectlight at door handle 735, it will be appreciated that light source 725could be mounted so as to project light also onto the ground region orother areas of the exterior of the vehicle as well as to the doorhandle. This could be accomplished by providing appropriate opticsbetween light source 725 and mirror structure 720. Additional lightsources could also be mounted so as to project light onto these areas.

The transflective (i.e., partially transmissive, partially reflective)rearview mirror described above allows the display of information to thedriver without removing a portion of the reflective coating. Thisresults in a more aesthetically pleasing appearance and allows themirror to appear as a contiguous reflector when the display is off. Anexample of a display particularly suited to this application is acompass display.

Many mirrors are sold each year which have the added feature ofdisplaying the heading of a vehicle using an alpha-numeric VacuumFluorescent Display (VFD) capable of displaying eight compass directions(N, S, E, W, NW, SW, NE, SE). These types of displays are used in manyother applications in motor vehicles such as radios and clocks. Thesedisplays have a glass cover over the phosphor digit segments. When usedwith a transflective mirror, the majority of the light from the VFD isnot transmitted through the mirror but reflected back to the display. Aportion of this reflected light is then reflected off both the top andbottom surfaces of the cover glass of the VFD and back through themirror. These multi-bounce reflections result is ghost or double imagesin the display which are highly undesired. As discussed above, asolution to this problem is to provide an anti-reflection coating on thecover glass of the VFD, however, such an anti-reflection coating adds tothe cost of the display. Other disadvantages of VFD displays are thatthey are expensive and fragile.

An LED alpha-numeric display is a viable alternative to a vacuumfluorescent display for use in a transflective mirror. As discussedabove, LED displays do not have a specular cover glass and thus do notsuffer from ghost reflection problems. Additionally, the areasurrounding the LEDs can be colored black to further aid in suppressingspurious reflections. LEDs also have the advantage of having extremelyhigh reliability and long life. Segmented alpha-numeric LED displays arecommercially available but are complicated to manufacture and it isdifficult to maintain segment to segment brightness and colorconsistency. Finally, it is also difficult to prevent light from onesegment from bleeding into another segment. LEDs are also only availablein saturated highly monochromatic colors, with the exception of somephosphor-LED combinations, which are currently very expensive. Manyautomotive manufacturers have display color schemes which are more broadspectrum and difficult, if not impossible to match with LEDtechnologies. Most cars manufactured in the United States have a bluedisplay color scheme, which could only be matched with blue LEDs whichare currently very expensive.

An alternative to a segmented LED or VFD display is described below thatovercomes the above problems associated with LEDs and VFDs. While thefollowing description is related to a compass display, the conceptscould readily be extended to a variety of information displays, such asa temperature display and various warning lights. The compass display isused as an example in the preferred embodiment because it bestillustrates the features and advantages of the invention. Also, thefollowing description will concentrate on the use of LEDs as thepreferred light source. However, many other light sources are alsoapplicable, such as incandescent bulbs or new emerging technologies suchas light emitting polymers and organic LEDs. The graphical, rather thanalpha-numerical, nature of this display clearly distinguishes it fromother alpha-numerical displays in a vehicle (such as the clock, etc.).Therefore, it will not look undesirable if this display does not matchthe color scheme of the VFD displays throughout the vehicle, allowingthe use of more efficient and cost effective displays. In fact, thecontrasting colors of the display should contribute to the aesthetics ofthe vehicle interior.

The display in the preferred embodiment consists of multiple LEDs, agraphical applique masking layer, and a transflective mirror. A frontview of the masking layer is shown in FIGS. 23A and 23B. The graphicalapplique shows eight points of a compass (801-808). The applique in FIG.23A includes all eight directions, however, only one of the eightdirections, as shown in FIG. 1 b, will be lit depending on the directionof travel. The region of the mirror containing the other directions willbe reflective and not indicate any content. A center graphic (809) maybe an emblem, such as the globe in FIGS. 23A and 23B, can be added forcosmetic appeal. The globe can be illuminated by an LED of a colorcontrasting the color of the direction indicators.

Various methods of controlling the segments are contemplated. In thesimplest form, only one of the LEDs behind the eight compass directionindicators is illuminated at a given time, depending on the direction oftravel. In another scheme, all eight indicators are lit dimly and theindicator corresponding to the current direction of travel is lit morebrightly than the other eight. In yet another scheme, bicolor LEDs areused and the LED indicator corresponding to the current direction oftravel is set to a different color than the other eight. A finalalternative would be to have only the indicator corresponding to thecurrent direction of travel lit, but gradually fade from one indicatorto another as the car changes directions.

The construction of the display is described with reference to FIGS. 24and 25. FIG. 24 shows the arrangement of LEDs on a circuit board andFIG. 25 shows an exploded view of the display assembly. The LEDs (812)are arranged on a circuit board (811) in a pattern corresponding to thelocations of the indicators and center graphic. LEDs (812) may be of thetype trade named “Pixar” by Hewlett Packard. Due to the loss of light inthe transflective coating, bright LEDs are needed. AlInGaP based LEDsare suitable for this application and are available in greed, red,amber, and various similar colors. Blue and green colors can be achievedby using InGaN LEDs. Although InGaN LEDs are currently expensive, thereare many fewer LEDs needed than would be used in a segmented display. Asan alternative to using packaged LEDs such as the “Pixar” LED, they canbe bonded to the circuit board directly using a technique commonly knownin the industry as Chip-On-Board.

The circuit board (811) is positioned behind the mirror using spacer(813). The spacer (813) serves multiple purposes. First, the spacerpositions the circuit board a distance from the mirror, ¼ inch forexample, such that the light from the LED fully covers the indicator.Second, the spacer prevents cross talk between indicators by preventinglight from one cavity from entering another cavity. To achieve this, thespacer should be made from a white, highly reflective material. At theleast, the spacer must be opaque. Finally, the spacer serves to helpreflect light exiting the LED at high angles back towards the indicator.This improves the efficiency of the system. The spacer may even beconstructed with a parabolic bowl surrounding the LED to mosteffectively direct light forward. A lambertian scattering surface on thespacer will also help diffuse the light and improve the uniformity ofthe indicator illumination. The empty region between the circuit board(811) and the mirror (815) formed by the openings in the spacer (813)may be filled with an epoxy or silicone containing a diffusant. Thiswill help further diffuse the light and help the indicators appear moreuniform.

An applique (814) is provided in a masking layer made of a thin materialwhich has a black matte mask covering all areas but the graphicalindicators. The regions for the graphic are a clear or somewhat whiteand diffuse. The applique may be formed by silk-screening the black maskpattern onto a film of diffuse plastic. Preferably, the side of theapplique facing the LEDs is also screened with a white ink. This willallow light which does not pass through the letters or graphical regionto reflect back onto the LED and spacer where it may then partiallyreflect back forward. Alternatively, the applique can be formed bydirectly silk screening the black mask onto the back surface of mirror(815). The manner by which such an applique may be constructed isdisclosed in U.S. Pat. No. 6,170,956, entitled “REARVIEW MIRRORDISPLAY,” filed on May 13, 1999, by Wayne J. Rumsey et al, the entiredisclosure of which is herein incorporated by reference.

Electrochromic mirrors tend to have a very high attenuation at specificwavelengths. For many commercially available electrochromic mirrors, thepeak attenuation occurs in the amber region of the visible spectrum.Curve A in FIG. 28 represents the spectral percentage transmission of aconventional electrochromic mirror in a darkened state. This makes ambercolored displays and indicia difficult to implement behind the mirror,as the brightness has to be increased substantially when the mirror isin its low reflectance state (i.e., its fully darkened state).

In accordance with one aspect of the present invention, amber light maybe generated using a red-green binary complementary light source insteadof by using a monochromatic amber light source. Because the red andgreen light is not as severely attenuated by the darkened electrochromicmirror element, the loss through the mirror is much less than wouldoccur when a monochromatic amber light source is used (see B and C inFIG. 28, which respectively represent the emission spectral of green andred LEDs). The red and green light nevertheless has the appearance ofamber light due to the mixing of the light from these two sources. Otherbinary complementary combinations and mix ratios could be used togenerate red-orange, yellow-green, or to accommodate otherelectrochromic chemistries. The two colors may need to be individuallycontrolled by the microprocessor used to control the mirror element asthe mirror is dimmed, since the attenuation versus wavelength functionsfor the two colors will likely be different.

This aspect of the present invention provides a rearview mirror assemblyincluding an electrochromic mirror element having a variablereflectivity and a display device positioned behind the electrochromicmirror element for displaying information in a first color (such asamber) through the electrochromic mirror element. The display devicecomprises at least one first light source for emitting light of a secondcolor (such as red) and at least one second light source for emittinglight of a third color (such as green), the second and third colorsbeing different from each other and different from the first color whilemixing together to form light of the first color.

FIG. 27 illustrates a preferred embodiment of this aspect of the presentinvention. As shown, an illumination device 1000 is positioned behind adisplay element 1010 for projecting light through the display element1010. Display element 1010 may be an indicia symbol that is etched outof the reflective layer on the rear element 114 of the electrochromicmirror, an applique or other indicia panel, or may be a dynamicallyvariable light shutter, such as a liquid crystal display (LCD) or anelectrochromic display provided on or near rear element 114. Examples ofdisplay elements in the form of an applique positioned behind anelectrochromic mirror are disclosed in commonly assigned U.S. patentapplication Ser. No. 09/586,813 entitled “REARVIEW MIRROR DISPLAY,”filed on Jun. 5, 2000, by Bradley L. Northman et al., the entiredisclosure of which is incorporated herein by reference.

Illumination device 1000 may include one or more light emittingpackages, such as those disclosed in commonly assigned U.S. Pat. No.6,335,548 entitled “SEMICONDUCTOR RADIATION EMITTER PACKAGE,” the entiredisclosure of which is incorporated herein by reference. In such apackage, a plurality of light sources 1002 and 1004 such as LED chips orother semiconductor radiation emitters are provided in the singlepackage and may be individually activated by selective application ofpower to different leads that are attached to the LED chips. In apreferred embodiment, at least two LED chips are included in thepackage, with one LED 1002 emitting red light and another LED 1004emitting green light so as to mix and form amber light that is emittedfrom the package. It will be appreciated by those skilled in the artthat illumination device 1000 may be positioned behind, about the edges,or slightly in front of display element 1010. Preferably, illuminationdevice 1000 is used to provide backlighting for display element 1010,which is most preferably an LCD element. The LCD element used could be atwisted nematic, super twist, active matrix, dichroic, dichroic phasechange, cholesteric, smectic, or ferroelectric type. Such backlighttechnology will work with any passive (non-light emitting) displaytechnology that acts as a light shutter. A high contrast ratio betweenthe transmissive and opaque states is desired. If light digits on a darkbackground are desired, a normally opaque twisted nematic display withparallel polarizers can be used. Since it is difficult to rotate allcolors of polarized light uniformly, these types of devices are usuallyoptimized for highest contrast at a single color. This limitation can beovercome by dissolving one or more dichroic dyes (generally acombination of dyes that produce black) in the liquid crystal media orusing a modified twisted nematic cell. One technique, which is useful toachieve high contrast ratios for all colors, is to use a normallytransmissive twisted nematic device with crossed polarizers with a blackopaque mask around all the digits. The digits in the voltage “off”condition would be transparent. The digits in the voltage “on” conditionwould be opaque. If all the digits were in the voltage “on” condition,the entire display area would be opaque because either the black maskaround all the digits or the voltage “on” opaque digits would absorb allthe light. In order to transmit light to display information in such adevice, the selected digits would be turned “off” such that no voltageis applied.

Although the preferred embodiment described above includes a separateillumination device 1000 and display element 1010, these elements may bemore or less integral with one another. Such a display may, for example,include a vacuum fluorescent display that utilizes a combination of redand green phosphors (or another combination of colors). Similarly, anLED display may be constructed that utilizes red and green or differentcolored LEDs. Thus, as broadly defined herein, the inventive displaystructure may include first and second “light sources” for emittinglight of first and second colors. Such light sources may includephotoluminescent light sources such as phosphorescent or fluorescentmaterials, and/or may include electroluminescent light sources,including, but not limited to, semiconductor radiation emitters such asLEDs, OLEDs, LEPs, etc.

As noted above, the display control firmware could be configured toincrease brightness of the display backlight as the electrochromicelement was darkened to maintain display readability and optionally toincrease brightness of the display during bright daylight conditions.Separate darkening and clearing time constants for each color LED may bedesired to model the electrochromic element so that the backlightintensity and color appear to be constant as the electrochromic mirrorreflectivity is changed. It should be noted that the reflector of theelectrochromic mirror may, but need not, be partially transmissive andpartially reflective as described above.

It should be noted that if the reflective layers that are discussedabove are applied over a rough rather than a smooth surface on the rearelement of the electrochromic structure, a reflector with more diffuserather than specular reflection will result. For instance, if one of thereflective or transflective coatings over an approximately full-wavelayer of fluorine-doped tin oxide (TEK 15 from LOF) is applied byatmospheric chemical vapor deposition, a reflector with significantdiffuse reflection will result. This is because the atmospheric chemicalvapor deposition process generally produces a much rougher surface whencompared to vacuum deposition processes such as for applying a layer ofITO at one-quarter or one-half wave thickness. Roughening the rearsubstrate will also produce diffuse reflection. For example, a diffusereflector can be made by either sandblasting or chemically etching glassto produce a frosted surface that is then overcoated with a reflector.It should be noted that if soda lime glass is used, the large area ofhighly alkaline glass surface created by the sandblasting process caninteract with certain electrochromic media even though it is overcoatedwith a thin metallic or transparent conductive layer. This interactiondoes not occur if borosilicate glass is used or if the rough surface onsoda lime glass is created by chemical etching. If the diffuse reflectoror transflector is made with a highly reflective material such assilver, silver alloys, rhodium, or aluminum, the reflector is white inappearance. If this reflector/transflector is incorporated into anelectrochromic element, a near black on white or dark blue/gray on whitecontrast can be achieved between the bleached and colored states.Specular reflection off of the front glass surface of the electrochromicelement can be reduced by lightly frosting or etching the surface orincorporating an anti-reflection coating on the front surface. This typeof electrochromic element construction could be used where black onwhite contrast is desired. For instance, a sign for displayinginformation could be made by constructing an array of these black onwhite elements or pixels and selectively coloring and bleaching theelements or pixels separately. More than one separately addressed ormultiplexed black on white pixel could be incorporated into anelectrochromic element, if desired. If a transflective coating is used,the electrochromic element could be backlit for night viewing. The thirdsurface metal reflector described above could be replaced with atransparent conductive layer such as ITO and the diffuse reflectivelayer could be on the fourth surface such as by coating a rough glassfourth surface with a silver layer and then painting it for protection.The reflective layer could also be a dichroic reflector.

One particularly useful implementation that would utilize a diffusereflecting electrochromic element would be display signs used to displaygas prices at a gas station. The display would consume low levels ofpower as compared with other variable light emitting-type displays thatmust emit illumination during daylight hours. Additionally, such anelectrochromic display would provide greater contrast than most of thosetypes of displays. The following are three examples of electrochromicelements produced with diffuse reflectors.

In the first example, soda lime glass having a thickness of 2.3 mm wascut into two inch by 5 inch pieces and sandblasted with aluminum oxideto frost the service. The sandblasted glass was coated with amulti-layer metal stack of about 450 Å of chrome, 100 Å of rhodium, and600 Å of silver/7 percent gold. Electrochromic elements were then madeusing fluorine-doped tin oxide (TEK 15) from Pilkington cut into twoinch by five inch pieces used as the front substrate, an epoxy sealaround the perimeter, and the metallized sandblasted glass as the backsubstrate. The TEK 15 and metal films were on the second and thirdsurfaces, respectively, with a 317 μm spacing between them. The elementswere then vacuum-filled with electrochromic fluid containing 34millimolar phenyl propyl viologen BF4 and DMP (dimethyl phenazine) withpropylene carbonate as the solvent along with a UV inhibitor andthickener. The fill-hole was plugged with a UV curing adhesive. Theelements were bright silver white in the uncolored state and colored toa nearly black appearance when 1.1 VDC was applied across theelectrochromic fluid media. The elements developed a blue colorovernight when stored at room temperature and the blue color became moreintense with time. It is believed that the sandblasting caused extensivefracturing of the alkaline soda lime glass surface that the metallicfilms did not completely overcoat and the exposed alkaline surfacecaused the electrochromic media to turn blue.

According to a second example, electrochromic elements were made as inthe above example, but with borosilicate glass substituted for the sodalime glass. ITO was used as a transparent conductor. The elements didnot develop a blue color after weeks of storage at room temperature.

A third example was made utilizing soda lime glass (2.3 mm thick) with atransparent conductive coating of fluorine-doped tin oxide (TEK 15)available from Pilkington, which was chemically etched by Eagle Glass toa gloss level of 120. The tin oxide surface was not protected andsurvived the etching process undamaged. An uncoated sheet of soda limeglass (2.3 mm thick) was chemically etched by Eagle Glass to a glosslevel of 30. The glass was cut to 3 inch by 3 inch pieces and washed.The 30-gloss glass was vacuum coated with a metal layer stack of about450 Å chrome, 100 Å rhodium, and 600 Å silver/7 percent gold. The glasswas then assembled using an epoxy primary seal with the TEK 15 on thesecond surface and the metal layer stack on the third surface. Thespacing between the two pieces of glass was about 137 μm. Theelectrochromic elements were vacuum filled with an electrochromic fluidthat gelled after filling and plugging the port opening with a UVcurable adhesive. The electrochromic fluid consisted of a 7 percentsolid gel formed by cross-linking Bisphenol A with a 1 to 10 isocyanatoethyl methacrylate/methyl methacrylate co-polymer at a 1.45 to 1isocyanate to alcohol ratio in polypropylene carbonate with 38millimolar methyl viologen BF4, 3.5 millimolar DMP (dimethyl phenozine),5.0 millimolar TMP (trimethyl phenozine) and 400 millimolar Uvinul N-35.The finished elements appeared bright silver/white in the uncoloredstate and black in the colored state. The electrochromic elements wereactivated for two days at 1.1 VDC and showed very little sign ofsegregation upon clearing.

The displays disclosed above in connection with FIGS. 9F and 9G may beutilized as a computer video monitor for a personal computer that isintegrated into the vehicle. Most preferably, the personal computer isintegrated into the rearview mirror assembly itself. Such a monitor maybe of the interlaced type, and may be an LCD or an electroluminescentdisplay.

When a computer video monitor is placed in front of the electrochromicmirror structure, the mirror is preferably constructed to provide aneutral gray appearance throughout its normal operating voltage range.Commonly assigned U.S. Pat. No. 6,020,987 discloses suitableelectrochromic media for obtaining such results. The entire disclosureof this patent is incorporated herein by reference. As theelectrochromic media darkens, it may be necessary to control the displaysuch that the display colors would change accordingly for anycompensation that is required to maintain constant display colorsthroughout the operating range of the electrochromic mirror.

By integrating a personal computer with a telematics system such as thatdisclosed in commonly assigned U.S. patent application Ser. No.09/827,304 filed Apr. 5, 2001, by Robert R. Tumbull et al. entitled“VEHICLE REARVIEW MIRROR ASSEMBLY INCORPORATING A COMMUNICATION SYSTEM,”the computer monitor may be used for displaying various forms ofinformation including e-mail messages and pages, turning indicators fornavigational systems; service reminders based on speed and mileage;vehicle heading; school, hospital zone warnings, weather, traffic, andemergency vehicle warnings; night vision displays; advertisements; stockquotes; and other information. Textual messages and other alphanumericdata and/or symbols may be superimposed over the video images displayedon the display device. If the vehicle is equipped with appropriate rearvision cameras, such as disclosed and described in commonly assignedU.S. patent application Ser. No. 09/001,855 filed on Dec. 31, 1997, byJon H. Bechtel et al. entitled “VEHICLE VISION SYSTEM,” now abandoned,and U.S. patent application Ser. No. 09/153,654 filed on Sep. 15, 1998,by Frederick T. Bauer et al. entitled “SYSTEMS AND COMPONENTS FORENHANCING REAR VISION FROM A VEHICLE,” now U.S. Pat. No. 6,550,949, theentire disclosures of which are incorporated herein by reference,coupling such cameras to the display would allow a video display of aview at the rear of the vehicle to assist drivers while connecting thevehicle to a trailer and for proportional steering with respect to thetrailer. Other graphics relating to the connection of the vehicle to atrailer may also be displayed.

Provisional use of video images may be disabled or enabled dependingupon the gear in which the vehicle is placed or based upon the speed orconstant direction maintained by the vehicle as determined by thecompass readout. Preferably, the displayed information fades in or outto reduce the amount of shock to the driver that would otherwise occurby the sudden appearance of a bright image on the rearview mirror. Therearview mirror assembly may include a track ball and/or other buttonsto allow the user to scroll through information displayed on the screento change what is displayed on the display screen, and to selectinformation displayed on the screen. Such track ball or other buttonsfor manipulating the display screen or functions within the personalcomputer may alternatively be provided remote from the rearview mirrorassembly, such as in the overhead console, floor console, doors,instrument panel, etc. to be in a location most convenient formanipulation by the driver or other vehicle occupants.

While the invention has been described in detail herein in accordancewith certain preferred embodiments thereof, many modifications andchanges therein may be effected by those skilled in the art withoutdeparting from the spirit of the invention. Accordingly, it is ourintent to be limited only by the scope of the appending claims and notby way of the details and instrumentalities describing the embodimentsshown herein.

1. A rearview mirror element for use in a vehicle, comprising: a firstsubstantially transparent substrate and a second substrate secured in aspaced apart relationship with respect to one another to form a chamberthere between, said second substrate comprising a layer of reflectivematerial at least approximately 200 Å thick comprising silver proximatea surface of said second substrate closest to said first substantiallytransparent substrate and a first layer of substantially transparentconductive material less than approximately 300 Å comprising indium tinoxide positioned between said layer of reflective material and saidfirst substantially transparent substrate, wherein the rearview mirrorelement exhibits at least 35% reflectivity.
 2. A rearview mirror elementas in claim 1 further comprising a second layer of substantiallytransparent conductive material positioned between said layer ofreflective material and said second substrate.
 3. A rearview mirrorelement as in claim 2 wherein said first layer of substantiallytransparent conductive material is indium tin oxide and said secondlayer of substantially transparent conductive material is indium tinoxide.
 4. A rearview mirror element as in claim 1 wherein said layer ofreflective material is silver.
 5. A rearview mirror element as in claim1 wherein said layer of reflective material is silver alloy.
 6. Arearview mirror element as in claim 1 wherein said first layer ofsubstantially transparent conductive material is indium tin oxide.
 7. Arearview mirror element as in claim 1 configured within an assemblyfurther comprising a light source positioned behind said secondsubstrate to through light through the rearview mirror element.
 8. Arearview mirror assembly as in claim 7 wherein a transmittancecharacteristic of the rearview mirror element is higher for a spectralband associated with emissions from said light source.
 9. A rearviewmirror element as in claim 1 further comprising at least one solutionphase electrochromic medium within the chamber.
 10. A rearview mirrorelement for use in a vehicle, comprising: a first substantiallytransparent substrate and a second substrate secured in a spaced apartrelationship with respect to one another to form a chamber therebetween, said second substrate comprising a layer of reflective materialat least approximately 200 Å thick comprising silver proximate a surfaceof said second substrate closest to said first substantially transparentsubstrate and a first layer of substantially transparent conductivematerial less than approximately 300 Å positioned between said layer ofreflective material and said first substantially transparent substrate,wherein the rearview mirror element exhibits at least 35% reflectivity.11. A rearview mirror element as in claim 10 further comprising a secondlayer of substantially transparent conductive material positionedbetween said layer of reflective material and said second substrate. 12.A rearview mirror element as in claim 11 wherein said first layer ofsubstantially transparent conductive material is indium tin oxide andsaid second layer of substantially transparent conductive material isindium tin oxide.
 13. A rearview mirror element as in claim 10 whereinsaid layer of reflective material is silver.
 14. A rearview mirrorelement as in claim 10 wherein said layer of reflective material issilver alloy.
 15. A rearview mirror element as in claim 10 wherein saidfirst layer of substantially transparent conductive material is indiumtin oxide.
 16. A rearview mirror element as in claim 10 configuredwithin an assembly further comprising a light source positioned behindsaid second substrate to project light through the rearview mirrorelement.
 17. A rearview mirror assembly as in claim 16 wherein atransmittance characteristic of the rearview mirror element is higherfor a spectral band associated with emissions from said light source.18. A rearview mirror element as in claim 10 further comprising at leastone solution phase electrochromic medium within the chamber.
 19. Arearview mirror element for use in a vehicle, comprising: a firstsubstantially transparent substrate and a second substrate secured in aspaced apart relationship with respect to one another to form a chamberthere between comprising at least one solution phase electrochromicmedium within the chamber, said second substrate comprising a layer ofreflective material at least approximately 200 Å thick comprising silverproximate a surface of said second substrate closest to said firstsubstantially transparent substrate and a first layer of substantiallytransparent conductive material less than approximately 300 Å positionedbetween said layer of reflective material and said first substantiallytransparent substrate, wherein the rearview mirror element exhibits atleast 35% reflectivity.
 20. A rearview mirror element as in claim 19further comprising a second layer of substantially transparentconductive material positioned between said layer of reflective materialand said second substrate.
 21. A rearview mirror element as in claim 20wherein said first layer of substantially transparent conductivematerial is indium tin oxide and said second layer of substantiallytransparent conductive material is indium tin oxide.
 22. A rearviewmirror element as in claim 19 wherein said layer of reflective materialis silver.
 23. A rearview mirror element as in claim 19 wherein saidlayer of reflective material is sliver alloy.
 24. A rearview mirrorelement as in claim 19 wherein said first layer of substantiallytransparent conductive material is indium tin oxide.
 25. A rearviewmirror element as in claim 19 configured within an assembly furthercomprising a light source positioned behind said second substrate toproject light through the rearview mirror element.
 26. A rearview mirrorassembly as in claim 25 wherein a transmittance characteristic of therearview mirror element is higher for a spectral band associated withemissions from said light source.